1 Enzymes Dr. Tagreed Osman

An enzyme is a protein catalyst that accelerates the speed of a chemical reaction by binding specifically to a substrate, forming a complex. This complex lowers the activation energy in the reaction without the enzyme becoming consumed or without changing the equilibrium of the reaction. Enzyme analysis is used to aid in diagnosis and treatment of disease.

3 Most enzymes with diagnostic applications function within the cells in which they are synthesized and since they have a large molecular mass, they do not cross cell membranes readily. Normally only small quantities of intracellular enzymes leak from cells into blood or other body fluids. Thus, an increase in enzyme activity when compared to the reference range can indicate pathological changes in certain cells and tissues.

4 The amounts are too low for enzyme mass to be measured, their activities can be monitored. In general, increased rather than decreased activities of enzymes are of diagnostic interest in body. Increased Enzyme activity levels in body fluids can reflect not only leakage from cells due to cellular injury, but also any changes in enzyme production rate, or actual enzyme induction due to metabolic or genetic states or proliferation of neoplasms. In the latter case, increased enzyme activity can be used as a tumor marker.

5 The following descriptions are relevant to enzyme analysis: Activity: rate of product produced or substrate consumed per unit of time; dependent on enzyme activity, substrate, activator, and coenzyme concentrations; temperature; pH; and other reaction conditions.

6 -Substrates: are the substances on which the enzymes act to convert them into products. Concentration of substrate plays a significant role in enzyme activity for formation of product. International unit (IU) of activity: quantity of enzyme able to convert one micromole (1µmol) of substrate per minute to product; often expressed as units per liter (U/L) or microunits per liter (µU/L).

7 -Activator: substance, such as a metal, that promotes formation of enzyme substrate complex and may affect enzyme activity for the formation of product. Coenzyme: complex molecule, such as dinucleotide (involved in electron transfer), that acts along with the substrate to aid in formation of product. Inhibitors: different types of interferences with the function of an enzyme that may be reversible or irreversible and lower the reaction rate of product formation.

8 Important properties of enzymes : 1.Produced by living cells, and are protein in nature except for riboenzymes. 2.Powerful catalyst. Catalyze the chemical reactions. 3.Enzymes have an (Active site) which is the substrate binding site 4.Enzymes are highly NOT absolutely specific. 5.Enzymes can be synthesized in an inactive form called PROENZYMES (zymogens). E.g. pepsinogen.

9 6.Iso-enzymes are those enzymes which have different structure but the same function. E.g. creatine phosphokinase (CPK)1………….. in brain (CPK)2…………… in heart (CPK)3…………… in muscle If these enzymes were found in the serum of the blood in high quantity, this indicates damage in tissue so enzymes a diagnostic value. 7. Enzymes can be used as drug.

10 Classes of Enzymes There are six classes of enzymes, describing the type of reaction involved: 1.Oxidoreductases: enzymes which catalyze the oxidation reduction reaction. 2.Transferases : enzymes which catalyze the transfer of C-containing, N-containing and sulfur containing groups 3.Hydrolases: enzymes that catalyze the breakdown of a certain compound by addition of water molecule.

11 4.Lyases: Enzymes which catalyze the breakdown of organic compound. 5.Ligases: enzymes which catalyze the connection between two molecules 6.Somerases: enzymes that catalyze the conversion between isomers. E.g. glucose and fructos

12 Enzymes as Biochemical Markers of Disease Damage to tissue can release different types of enzymes based on their location. For example, mild inflammation of the liver reversibly increases the permeability of the cell membrane and releases cytoplasmic enzymes such as lactate dehydrogenase (LD), alkaline phosphatase (ALP), and aspartate transaminase (AST), while necrosis will release mitochondrial sources of alanine transaminase (ALT) as well as AST.

13 Serum enzymes in disease Myocardial infarction Muscle disease Liver disease Bone disease Haematological disorders