1. UNIT II: Bioenergetics and Carbohydrate Metabolism CHAPTER 13: PENTOSE PHOSPHATE PATHWAY AND NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE

2. Dr. M. Alzaharna 2016 I. OVERVIEW The pentose phosphate pathway (also called the hexose monophosphate shunt) occurs in the cytosol of the cell. It includes two irreversible oxidative reactions, followed by a series of reversible sugar–phosphate interconversions (Figure 13.1). No adenosine triphosphate (ATP) is directly consumed or produced in the cycle. Carbon 1 of glucose 6-phosphate is released as CO 2, and two reduced nicotinamide adenine dinucleotide phosphates (NADPHs) are produced for each glucose 6-phosphate molecule entering the oxidative part of the pathway. The rate and direction of the reversible reactions of the pentose phosphate pathway are determined by the supply of and demand for intermediates of the cycle. 2

3. Dr. M. Alzaharna 2016 Figure 13.1. Hexose monophosphate pathway shown as a component of the metabolic map

4. Dr. M. Alzaharna 2016 I. OVERVIEW The pathway provides a major portion of the body’s NADPH, which functions as a biochemical reductant. It also produces ribose 5-phosphate, required for the biosynthesis of nucleotides, and provides a mechanism for the metabolic use of five-carbon sugars obtained from the diet or the degradation of structural carbohydrates 4

5. Dr. M. Alzaharna 2016 II. IRREVERSIBLE OXIDATIVE REACTIONS The oxidative portion of the pentose phosphate pathway consists of three reactions that lead to the formation of ribulose 5-phosphate, CO 2, and two molecules of NADPH for each molecule of glucose 6-phosphate oxidized (Figure 13.2). This portion of the pathway is particularly important in: the liver, lactating mammary glands, and adipose tissue, which are active in the NADPH-dependent biosynthesis of fatty acids; in the testes, ovaries, placenta, and adrenal cortex, which are active in the NADPH-dependent biosynthesis of steroid hormones; and in red blood cells (RBCs), which require NADPH to keep glutathione reduced 5

6. Dr. M. Alzaharna 2016 Figure 13.2: Reactions of the pentose phosphate pathway. Enzymes numbered above are: 1, 2) glucose 6- phosphate dehydrogenase and 6-phosphogluconolactone hydrolase, 3) 6-phosphogluconate dehydrogenase, 4) ribose 5-phosphate isomerase, 5) phosphopentose epimerase, 6 and 8) transketolase (coenzyme: thiamine pyrophosphate), and 7) transaldolase. Δ2C = two carbons are transferred in transketolase reactions; Δ3C = three carbons are transferred in the transaldolase reaction. This can be represented as: 5C sugar + 5C sugar Δ2C 7C sugar + 3C sugar Δ3C 4C sugar + 6C sugar. NADP(H) = nicotinamide adenine dinucleotide phosphate; P = phosphate.

7. Dr. M. Alzaharna 2016 II. IRREVERSIBLE OXIDATIVE REACTIONS A. Dehydrogenation of glucose 6- phosphate Glucose 6-phosphate dehydrogenase (G6PD) catalyzes an irreversible oxidation of glucose 6-phosphate to 6- phosphogluconolactone in a reaction that is specific for oxidized NADP (NADP + ) as the coenzyme. The pentose phosphate pathway is regulated primarily at the G6PD reaction. NADPH is a potent competitive inhibitor of the enzyme, and, under most metabolic conditions, the ratio of NADPH/NADP + is sufficiently high to greatly inhibit enzyme activity. However, with increased demand for NADPH, the ratio of NADPH/ NADP + decreases, and flux through the cycle increases in response to the enhanced activity of G6PD. Insulin upregulates expression of the gene for G6PD, and flux through the pathway increases in the absorptive state 7

8. Dr. M. Alzaharna 2016 II. IRREVERSIBLE OXIDATIVE REACTIONS B. Formation of ribulose 5-phosphate 6-Phosphogluconolactone is hydrolyzed by 6- phosphogluconolactone hydrolase. The reaction is irreversible and not rate limiting. The oxidative decarboxylation of the product, 6- phosphogluconate, is catalyzed by 6-phosphogluconate dehydrogenase. This irreversible reaction produces: a pentose sugar–phosphate (ribulose 5-phosphate), CO 2 (from carbon 1 of glucose), and a second molecule of NADPH (Figure 13.2). 8

9. Dr. M. Alzaharna 2016 III. REVERSIBLE NONOXIDATIVE REACTIONS The nonoxidative reactions of the pentose phosphate pathway occur in all cell types synthesizing nucleotides and nucleic acids. These reactions catalyze the interconversion of sugars containing three to seven carbons (Figure 13.2). These reversible reactions permit ribulose 5-phosphate to be converted either: to ribose 5-phosphate (needed for nucleotide synthesis) or to intermediates of glycolysis (that is, fructose 6-phosphate and glyceraldehyde 3-phosphate). For example, many cells that carry out reductive biosynthetic reactions have a greater need for NADPH than for ribose 5- phosphate. 9

10. Dr. M. Alzaharna 2016 III. REVERSIBLE NONOXIDATIVE REACTIONS In this case, transketolase (which transfers two-carbon units) and transaldolase (which transfers three –carbon units) convert the ribulose 5-phosphate produced as an end product of the oxidative reactions to glyceraldehyde 3-phosphate and fructose 6-phosphate, which are glycolytic intermediates. In contrast, when the demand for ribose for nucleotides and nucleic acids is greater than the need for NADPH, the nonoxidative reactions can provide the ribose 5-phosphate from glyceraldehyde 3-phosphate and fructose 6-phosphate in the absence of the oxidative steps (Figure 13.3). 10

11. Dr. M. Alzaharna 2016 Figure 13.3: Formation of ribose 5-phosphate from intermediates of glycolysis. P = phosphate; DHAP = dihydroxyacetone phosphate.

12. Dr. M. Alzaharna 2016 IV. USES OF NADPH The coenzyme NADPH differs from nicotinamide adenine dinucleotide (NADH) only by the presence of a phosphate group on one of the ribose units (Figure 13.4). This seemingly small change in structure allows NADPH to interact with NADPH-specific enzymes that have unique roles in the cell. This section summarizes some important NADP + and NADPH specific functions in reductive biosynthesis and detoxification reactions 12

13. Dr. M. Alzaharna 2016 Figure 13.4: Structure of reduced nicotinamide adenine dinucleotide phosphate (NADPH).

14. Dr. M. Alzaharna 2016 IV. USES OF NADPH A. Reductive biosynthesis NADPH can be thought of as a high-energy molecule, much in the same way as NADH. However, the electrons of NADPH are destined for use in reductive biosynthesis, rather than for transfer to oxygen as is the case with NADH. Thus, in the metabolic transformations of the pentose phosphate pathway, part of the energy of glucose 6-phosphate is conserved in NADPH, a molecule with a negative reduction potential, that, therefore, can be used in reactions requiring an electron donor, such as fatty acid and steroid synthesis. 14

15. Dr. M. Alzaharna 2016 IV. USES OF NADPH B. Reduction of hydrogen peroxide Hydrogen peroxide (H 2 O 2 ) is one of a family of reactive oxygen species (ROS) that are formed from the partial reduction of molecular oxygen (Figure 13.5A). These compounds are formed continuously as byproducts of aerobic metabolism, through reactions with drugs and environmental toxins, or when the level of antioxidants is diminished, all creating the condition of oxidative stress. The highly reactive oxygen intermediates can cause serious chemical damage to DNA, proteins, and unsaturated lipids and can lead to cell death. ROS have been implicated in a number of pathologic processes, including reperfusion injury, cancer, inflammatory disease, and aging. The cell has several protective mechanisms that minimize the toxic potential of these compounds 15

16. Dr. M. Alzaharna 2016 Figure 13.5: A. Formation of reactive intermediates from molecular oxygen. e - = electrons. B. Actions of antioxidant enzymes. G-SH = reduced glutathione; G-S-S-G = oxidized glutathione. (See Figure 13.6B for the regeneration of G-SH.)

17. Dr. M. Alzaharna 2016 IV. USES OF NADPH B. Reduction of hydrogen peroxide 1.Enzymes that catalyze antioxidant reactions: Reduced glutathione (G-SH), present in most cells, can chemically detoxify H 2 O 2 (Figure 13.5B). The cell regenerates G-SH in a reaction catalyzed by glutathione reductase, using NADPH as a source of reducing equivalents. Thus, NADPH indirectly provides electrons for the reduction of H 2 O 2 (Figure 13.6). Note: RBCs are totally dependent on the pentose phosphate pathway for their supply of NADPH because, unlike other cell types, RBCs do not have an alternate source for this essential coenzyme. Additional enzymes, such as superoxide dismutase and catalase, catalyze the conversion of other reactive oxygen intermediates to harmless products (see Figure 13.5B). As a group, these enzymes serve as a defense system to guard against the toxic effects of ROS. 17

18. Dr. M. Alzaharna 2016 Figure 13.6: A. Structure of reduced glutathione (G-SH). B. Glutathione-mediated reduction of hydrogen peroxide (H 2 O 2 ) by reduced nicotinamide adenine dinucleotide phosphate (NADPH). G-S-S-G = oxidized glutathione.

19. Dr. M. Alzaharna 2016 IV. USES OF NADPH B. Reduction of hydrogen peroxide 2.Antioxidant chemicals: A number of intracellular reducing agents, such as ascorbate, vitamin E, and β-carotene, are able to reduce and, thereby, detoxify reactive oxygen intermediates in the laboratory. Consumption of foods rich in these antioxidant compounds has been correlated with a reduced risk for certain types of cancers as well as decreased frequency of certain other chronic health problems. However, clinical trials with antioxidants as dietary supplements have failed to show clear beneficial effects. In the case of dietary supplementation with β-carotene, the rate of lung cancer in smokers increased rather than decreased. Thus, the health-promoting effects of dietary fruits and vegetables likely reflect a complex interaction among many naturally occurring compounds, 19

20. Dr. M. Alzaharna 2016 IV. USES OF NADPH C. Cytochrome P450 monooxygenase system Monooxygenases (mixed-function oxidases) incorporate one atom from molecular oxygen into a substrate (creating a hydroxyl group), with the other atom being reduced to water. In the cytochrome P450 monooxygenase system, NADPH provides the reducing equivalents required by this series of reactions (Figure 13.7). This system performs different functions in two separate locations in cells. The overall reaction catalyzed by a cytochrome P450 enzyme is: where R may be a steroid, drug, or other chemical. 20

21. Dr. M. Alzaharna 2016 Figure 13.7: Cytochrome P450 monooxygenase cycle (simplified). Electrons (e - ) move from NADPH to FAD to FMN of the reductase and then to the heme iron (Fe) of the P450 enzyme. FAD = flavin adenine dinucleotide; FMN = flavin mononucleotide; NADPH = reduced nicotinamide adenine dinucleotide phosphate.

22. Dr. M. Alzaharna 2016 IV. USES OF NADPH C. Cytochrome P450 monooxygenase system 1.Mitochondrial system: An important function of the cytochrome P450 monooxygenase system found associated with the inner mitochondrial membrane is the biosynthesis of steroid hormones. The liver uses this same system in bile acid synthesis and the hydroxylation of cholecalciferol to 25-hydroxycholecalciferol (vitamin D3), and the kidney uses it to hydroxylate vitamin D3 to its biologically active 1,25-dihydroxylated form 22

23. Dr. M. Alzaharna 2016 IV. USES OF NADPH C. Cytochrome P450 monooxygenase system 2.Microsomal system: An extremely important function of the microsomal cytochrome P450 monooxygenase system found associated with the membrane of the smooth endoplasmic reticulum (particularly in the liver) is the detoxification of foreign compounds (xenobiotics). A xenobiotic is a foreign chemical substance found within an organism that is not normally naturally produced by or expected to be present within that organism These include numerous drugs and such varied pollutants as petroleum products and pesticides. CYP enzymes of the microsomal system (for example, CYP3A4), can be used to hydroxylate these toxins. The purpose of these modifications is two-fold. First, it may itself activate or inactivate a drug and second, make a toxic compound more soluble, thereby facilitating its excretion in the urine or feces. 23

24. Dr. M. Alzaharna 2016 IV. USES OF NADPH D. Phagocytosis by white blood cells Phagocytosis is the ingestion by receptor-mediated endocytosis of microorganisms, foreign particles, and cellular debris by cells such as neutrophils and macrophages (monocytes). It is an important defense mechanism, particularly in bacterial infections. Neutrophils and monocytes are armed with both oxygen- independent and oxygen-dependent mechanisms for killing bacteria 1.Oxygen-independent mechanism: Oxygen-independent mechanisms use pH changes in phagolysosomes and lysosomal enzymes to destroy pathogens 24

25. Dr. M. Alzaharna 2016 IV. USES OF NADPH D. Phagocytosis by white blood cells 2.Oxygen-dependent system: Oxygen-dependent mechanisms include the enzymes NADPH oxidase and myeloperoxidase (MPO) that work together in killing bacteria (Figure 13.8). Overall, the MPO system is the most potent of the bactericidal mechanisms. An invading bacterium is recognized by the immune system and attacked by antibodies that bind it to a receptor on a phagocytic cell. After internalization of the microorganism has occurred, NADPH oxidase, located in the leukocyte cell membrane, is activated and reduces O 2 from the surrounding tissue to superoxide, a free radical, as NADPH is oxidized. The rapid consumption of O 2 that accompanies formation of is referred to as the “respiratory burst.” 25

26. Dr. M. Alzaharna 2016 Figure 13.8: Phagocytosis and the oxygen- dependent pathway of microbial killing. IgG = the antibody immunoglobulin G; NADPH = reduced nicotinamide adenine dinucleotide phosphate; O2 dot over bar = superoxide; HOCl = hypochlorous acid; OH = hydroxyl radical.

27. Dr. M. Alzaharna 2016 IV. USES OF NADPH D. Phagocytosis by white blood cells Next, is converted to H 2 O 2 (a ROS), either spontaneously or catalyzed by superoxide dismutase. In the presence of MPO, a heme-containing lysosomal enzyme present within the phagolysosome, peroxide plus chloride ions are converted to hypochlorous acid ([HOCl] the major component of household bleach), which kills the bacteria. The peroxide can also be partially reduced to the hydroxyl radical (OH), a ROS, or be fully reduced to water by catalase or glutathione peroxidase. Note: Deficiencies in MPO do not confer increased susceptibility to infection because peroxide from NADPH oxidase is bactericidal. 27

28. Dr. M. Alzaharna 2016 IV. USES OF NADPH E. Synthesis of nitric oxide Nitric oxide (NO) is recognized as a mediator in a broad array of biologic systems. NO is the endothelium-derived relaxing factor, which causes vasodilation by relaxing vascular smooth muscle. NO also acts as a neurotransmitter, prevents platelet aggregation, and plays an essential role in macrophage function. NO has a very short half-life in tissues (3–10 seconds) because it reacts with oxygen and superoxide and then is converted into nitrates and nitrites including peroxynitrite (O=NOO – ), a reactive nitrogen species (RNS). 28

29. Dr. M. Alzaharna 2016 Figure 13.9: Synthesis and some of the actions of nitric oxide (NO). NADPH = reduced nicotinamide adenine dinucleotide phosphate. [Note: Flavin mononucleotide, flavin adenine dinucleotide, heme, and tetrahydrobiopterin are additional coenzymes required by NOS.]

30. Dr. M. Alzaharna 2016 V. GLUCOSE 6-PHOSPHATE DEHYDROGENASE DEFICIENCY G6PD deficiency is a hereditary disease characterized by hemolytic anemia caused by the inability to detoxify oxidizing agents. G6PD deficiency is the most common disease-producing enzyme abnormality in humans, affecting more than 400 million individuals worldwide. This deficiency has the highest prevalence in the Middle East, tropical Africa and Asia, and parts of the Mediterranean. G6PD deficiency is X linked and is, in fact, a family of deficiencies caused by a number of different mutations in the gene coding for G6PD. Only some of the resulting protein variants cause clinical symptoms. 30

31. Dr. M. Alzaharna 2016 V. GLUCOSE 6-PHOSPHATE DEHYDROGENASE DEFICIENCY The jaundice, which may be severe, typically results from increased production of unconjugated bilirubin (see p. 285). The life span of individuals with a severe form of G6PD deficiency may be somewhat shortened as a result of complications arising from chronic hemolysis. This negative effect of G6PD deficiency has been balanced in evolution by an advantage in survival—an increased resistance to Plasmodium falciparum malaria. [Note: Sickle cell trait and β-thalassemia minor also confer resistance to malaria.] 31

32. Dr. M. Alzaharna 2016 V. GLUCOSE 6-PHOSPHATE DEHYDROGENASE DEFICIENCY A. Role of glucose 6-phosphate dehydrogenase in red blood cells Diminished G6PD activity impairs the ability of the cell to form the NADPH that is essential for the maintenance of the G-SH pool. This results in a decrease in the cellular detoxification of free radicals and peroxides formed within the cell (Figure 13.10). G-SH also helps maintain the reduced states of sulfhydryl groups in proteins, including hemoglobin. Oxidation of those sulfhydryl groups leads to the formation of denatured proteins that form insoluble masses (called Heinz bodies) that attach to RBC membranes (Figure 13.11). Additional oxidation of membrane proteins causes RBCs to be rigid (less deformable), and they are removed from the circulation by macrophages in the spleen and liver. Although G6PD deficiency occurs in all cells of the affected individual, it is most severe in RBCs, where the pentose phosphate pathway provides the only means of generating NADPH. 32

33. Dr. M. Alzaharna 2016 Figure 13.10: Pathways of glucose 6-phosphate metabolism in the erythrocyte. NADP(H) = nicotinamide adenine dinucleotide phosphate; G-SH = reduced glutathionine; G-S-S-G = oxidized glutathionine; PPP = pentose phosphate pathway.

34. Dr. M. Alzaharna 2016 Figure 13.11: Heinz bodies in erythrocytes of a patient with glucose 6-phosphate dehydrogenase deficiency.

35. Dr. M. Alzaharna 2016 V. GLUCOSE 6-PHOSPHATE DEHYDROGENASE DEFICIENCY A. Role of glucose 6-phosphate dehydrogenase in red blood cells Other tissues have alternative sources for NADPH production (such as NADP + -dependent malate dehydrogenase [malic enzyme]; that can keep G-SH reduced. The RBC has no nucleus or ribosomes and cannot renew its supply of the enzyme. Thus, RBCs are particularly vulnerable to enzyme variants with diminished stability 35

36. Dr. M. Alzaharna 2016 V. GLUCOSE 6-PHOSPHATE DEHYDROGENASE DEFICIENCY B. Precipitating factors in glucose 6-phosphate dehydrogenase deficiency Most individuals who have inherited one of the G6PD mutations do not show clinical manifestations (that is, they are asymptomatic). However, some patients with G6PD deficiency develop hemolytic anemia if they are treated with an oxidant drug, ingest fava beans, or contract a severe infection. 1.Oxidant drugs: Commonly used drugs that produce hemolytic anemia in patients with G6PD deficiency are best remembered from the mnemonic AAA: antibiotics (for example, sulfamethoxazole and chloramphenicol), antimalarials (for example, primaquine but not chloroquine or quinine ), and antipyretics (for example, acetanilid but not acetaminophen). 36

37. Dr. M. Alzaharna 2016 V. GLUCOSE 6-PHOSPHATE DEHYDROGENASE DEFICIENCY B. Precipitating factors in glucose 6- phosphate dehydrogenase deficiency 2.Favism: Some forms of G6PD deficiency, for example the Mediterranean variant, are particularly susceptible to the hemolytic effect of the fava (broad) bean, a dietary staple in the Mediterranean region. Favism, the hemolytic effect of ingesting fava beans, is not observed in all individuals with G6P D deficiency, but all patients with favism have G6PD deficiency. 3.Infection: Infection is the most common precipitating factor of hemolysis in G6PD deficiency. The inflammatory response to infection results in the generation of free radicals in macrophages, which can diffuse into the RBC and cause oxidative damage. 37

38. Dr. M. Alzaharna 2016 V. GLUCOSE 6-PHOSPHATE DEHYDROGENASE DEFICIENCY C. Properties of the variant enzymes Almost all G6PD variants are caused by point mutations in the gene for G6PD. Some mutations do not disrupt the structure of the enzyme’s active site and, therefore, do not affect enzymic activity. However, many mutant enzymes show altered kinetic properties. For example, variant enzymes may show decreased catalytic activity, decreased stability, or an alteration of binding affinity for NADP +, NADPH, or glucose 6-phosphate. The severity of the disease usually correlates with the amount of residual enzyme activity in the patient’s RBC. For example, variants can be classified as shown in Figure 13.12. 38

39. Dr. M. Alzaharna 2016 Figure 13.12: Classification of glucose 6-phosphate dehydrogenase (G6PD) deficiency variants. Note: Class V variants (not shown in table) result in overproduction of G6PD.

40. Dr. M. Alzaharna 2016 Figure 13.13: Decline of erythrocyte glucose 6-phosphate dehydrogenase (G6PD) activity with cell age for the three most commonly encountered forms of the enzyme.

41. Dr. M. Alzaharna 2016 V. GLUCOSE 6-PHOSPHATE DEHYDROGENASE DEFICIENCY D. Molecular biology of glucose 6- phosphate dehydrogenase The cloning of the gene for G6PD and the sequencing of its DNA have permitted the identification of mutations that cause G6PD deficiency. More than 400 different G6PD variants have been identified, a finding that explains the numerous biochemical and clinical phenotypes that have been described. Most mutations that result in enzymic deficiency are missense mutations in the coding region. Both G6PD A – and G6PD Mediterranean represent mutant enzymes that differ from the respective normal variants by a single amino acid. Large deletions or frameshift mutations have not been identified, suggesting that complete absence of G6PD activity is probably lethal 41

42. Dr. M. Alzaharna 2016 Summary The pentose phosphate pathway consists of 2 irreversible oxidative reactions followed by a series of reversible sugar-phosphate interconversions No ATP is directly consumed or produced in the cycle The oxidative portion is particularly important in liver & mammary glands, which are active in biosynthesis of fatty acids, in adrenal cortex, which is active in NADPH-dependent synthesis of steroids, & in erythrocytes, which require NADPH to keep glutathione reduced G-6-P is irreversibly converted to ribulose-5-P, & 2 NADPH are produced. The regulated step is G6PD, which is strongly inhibited by NADPH Reversible nonoxidative reactions interconvert sugars. This part of pathway is the source of ribose 5-P required for nt & nucleic acid synthesis Because reactions are reversible, they can be entered from F-6-P & GA 3P (glycolytic intermediates) if ribose is needed & G6PD is inhibited

43. Dr. M. Alzaharna 2016 NADPH is a source of reducing equivalents in reductive biosynthesis, such as production of fatty acids & steroids. It is also required for reduction of hydrogen peroxide, providing the reducing equivalents required by glutathione (GSH). GSH is used by glutathione peroxidase to reduce peroxide to water. The oxidized glutathione is reduced by glutathione reductase, using NADPH as the source of electrons NADPH provides reducing equivalents for cyt-P450 monooxygenase system, which is used in hydroxylation of steroids to produce steroid hormones, bile acid synthesis by liver, & activation of vitamin D. the system also detoxify foreign compounds, e.g., drugs & varied pollutants, including carcinogens, pesticides, & petroleum products Summary

44. Dr. M. Alzaharna 2016 NADPH provides reducing equivalents for phagocytes in the process of eliminating invading microorganisms NADPH oxidase uses molecular oxygen & NADPH to produce superoxide radicals, which, in turn, can be converted to peroxide, hypochlorous acid, & hydroxyl radicals. Myeloperoxidase is an important enzyme in this pathway A genetic defect in NADPH oxidase causes chronic granulomatosis, a disease characterized by severe, persistent, chronic pyogenic infections NADPH is required for synthesis of nitric oxide (NO), an important molecule that causes vasodilation by relaxing vascular smooth muscle, acts as a kind of neurotransmitter, prevents platelet aggregation, & helps mediate macrophage bactericidal activity Summary

45. Dr. M. Alzaharna 2016 G6PD deficiency is a genetic disease characterized by hemolytic anemia. It impairs ability of cell to form NADPH that is essential for maintenance of reduced glutathione pool. Cells most affected are RBCs because they do not have additional sources of NADPH Free radicals & peroxides formed within the cells can’t be neutralized, causing denaturation of protein (e.g., Hb, forming Heinz bodies) & membrane proteins. Cells become rigid, & they are removed by reticuloendothelial system of spleen & liver Hemolytic anemia can be caused by production of free radicals & peroxides following the taking of oxidant drugs, ingestion of fava beans, or severe infections Babies with G6PD deficiency may experience neonatal jaundice appearing 1-4 days after birth Degree of severity of anemia depends on location of mutation in G6PD gene. Class I mutations are the most severe (e.g., G6PD Mediterranean). They are often associated with chronic non-spherocytic anemia. Class III mutations (e.g., G6PD A-) cause a more moderate form of the disease Summary

46. Dr. M. Alzaharna 2016 46