Overview of Fuel Oxidation II A/Prof Gareth Denyer

Beta-oxidation Fatty acids blood cytoplasm Fatty acyl-CoA Trapping involves attaching the FA to CoA Fatty acyl-CoA CoA matrix Swapping the CoA for carnitine allows the FA to get into the mitochondrial matrix Carnitine often sold as a ‘fat metaboliser’. Claim is that carnitine will help the transport of FA into matrix…. And that this will help burn fat. Sorry, unless you’re specifically deficient in carnitine, it doesn’t actually work..  Hydrogens removed by NAD NAD NADH Fatty acyl-CoA (2 less carbons in FA) Acetyl-CoA

NAD Nicotinamide adenine dinucleotide –Adenine nucleotide attached back-to- back with a nucleotide that has nicotinamide as the “base” Nicotinamide is made from nicotinic acid –More commonly called NIACIN or Vitamin B 3 –A supplement in our cereals! –Vital for fuel oxidation NAD not only rips hydrogens out of the fuels, it carries them around afterwards. –Actually rips out hydride ions – proton plus two electrons PP Adenine base ribose Nicotinamide ribose

Beta-Oxidation As the fatty acids lose hydrogens, they start to break up.. –They do so in a very regular way – by the loss of acetate groups –These acetate groups are also carried around on CoA – so the acetate does not exist ‘by itself’ but rather as acetyl-CoA As a result, the FA becomes shorter by two carbons The process of H stripping and FA getting shorter happens sequentially –Until all the FA is converted into Acetyl CoA The scheme is often shown as a ‘sprial’ of degradation. –With AcCoA and NADH coming off and NAD and CoA coming in. Fatty acyl-CoA CoA Acetyl-CoA NADH CoA NAD FA(n- 2 )-CoA FA(n- 4 )-CoA FA(n- 6 )-CoA FA(n- 8 )-CoA

Beta-Oxidation Sequential cutting up of fatty acids –Into Acetyl CoA –With the release of NADH And consumption of CoA and NAD, of course! Occurs in the mitochondria But what happens to the Acetyl CoA?

Glucose Oxidation Glucose blood cytoplasm Glucose Trapping involves phosphorylation Which uses a little ATP CO 2 Transport into the cells requires GLUTs There are several forms of GLUT Hydrogens removed by NAD again… pyruvate breaks up NAD NADH pyruvate Acetyl-CoA Glucose 6-phosphate More investment of ATP… and a bit of rearrangement Fructose 1,6- bisphosphate NAD rips out Hs, 6 carbon sugar breaks up into the 3-carbon pyruvate, and ATP is produced pyruvate ADP ATP matrix

Glucose Oxidation First part happens in the cytoplasm –This section returns a very small amount of ATP –2 ATPs per glucose More energy will be extracted from pyruvate –Pyruvate transported into the mitochondria and further oxidised

The Krebs Cycle Fuels Acetyl-CoA NADH NAD CO 2 Also called the Tricarboxylic acid (TCA) cycle or the Citric Acid cycle –DON’T PANIC… all you need to know is the POINT of the cycle It’s function is to rip out every last hydrogen and fully oxidise the carbons in acetyl CoA –So heaps of NADH is generated –And the carbon atoms in the fuels are made into carbon dioxide So after all this, the fuels have been converted into carbon dioxide and Hs (which are carried around on NAD) BUT WHAT’S THE POINT Pyruvate and FA-CoA

Energy in Hydrogen! Hydrogen + Oxygen  Water –Liberates a LOT of energy! –That’s how the Space Shuttle works! We’re going to react the hydrogen in NADH with oxygen –But we’re going to do it in a controlled, stepwise manner in which the energy is harnessed as ATP

e - Transport and H + pumping NADH passes H to a chain of electron transporting complexes in the inner mitochondrial membrane –The Hs are passed down the chain to oxygen As the Hs move down the chain, protons are pumped from the matrix into the cytoplasm –This creates a PROTON GRADIENT –Also called a pressure of protons The inner mitochondrial membrane is impermeable to protons –This helps maintain the pressure! Note that NAD is regenerated by this NADHNAD O2O2 H2OH2O H+H+ H+H+ H+H+ H+H+

Making ATP with H + gradient The protons flow (under pressure!) through the F0 channel in the inner mito membrane –As they come in, they cause another protein (the banana shaped gamma-subunit!) to rotate –The gamma subunit interacts with the subunits of the F1-ATPase to generate ATP from ADP and phosphate The ATP leaves the mitochondria – it does most of its work in the cytoplasm –When ATP is used to do work, it turns back into ADP and phosphate –The ADP and phosphate come back into the mitocondria to complete the cycle H+H+ ATPADP H+H+ ATPADP

NADH NAD O2O2 H2OH2O H+H+ H+H+ H+H+ H+H+ Fuels Acetyl-CoA CO 2 ATPADP H+H+