Complex IV is also known as cytochrome oxidase and contains cytochromes a and a3 as shown in Figure 8.19. The cytochromes are made up of two heme groups bound to different regions of the same large protein, which are therefore functionally and spectrally different. In addition, complex IV contains two copper ions, CuA and CuB, which are…
This is also called cytochrome bc1 complex or ubiquinone, cytochrome-oxidoreductase. This couples the transfer of electrons from ubiquinol (QH2) to cytochrome c with the vectorial transport of protons from the matrix to the intermembrane space. Net equation for the redox reactions of Q cycle: QH2 + 2Cyt c1 (oxidised) + 2H + N → Q…
Complex II is called succinate dehydrogenase complex. It is the only membrane-bound enzyme in TCA. Complex II is smaller and simpler than complex I. However, it contains two types of prosthetic groups and at least four different proteins. To the first protein FAD is covalently bound and Fe-S centre with four Fe atoms. In addition,…
Helmut Beinert first discovered that the iron is present in heme and associated with inorganic sulphur atoms or with sulphur atoms of cysteine residues in the proteins or both. These iron sulphur (Fe-S) centres range from simple structures with single Fe atom coordinated with four cys-SH groups to more complex Fe-S centres with two or…
ELECTRON CARRIERS Electron carriers in the electron transport chain are the following:
Glycogen degradation requires the following two reactions: Removal of glucose forms the non-reducing ends of glycogen. Using inorganic phosphate (Pi), glycogen phosphorylase cleaves the (1,4) linkages on the outer branches of glycogen to yield glucose-1-phosphate. Glycogen phosphorylase stops when it comes within four glucose residues of a branch point. A glycogen molecule that has been degraded…
When the chain is lengthened to a minimum of eleven glucose residues, the branching enzyme amylo (α 1-4, α 1-6) transglucosidase (Figure 8.12) (glucosyl α 4, 6-transferase) transfers a small fragment of five to eight glucose residues from the non-reducing end of the glycogen chain by breaking α 1-4 linkage to another glucose residue, where…
Glycogen synthase is required for the formation of α 1-4 glycosidic linkages. This enzyme transfers the glucose from UDP-glucose to the glycogen primer to form α 1-4 linkages. The UDP released can be converted again to UTP with the help of nucleotide diphosphate kinase.
A small fragment of pre-existing glycogen must act as a primer to initiate glycogen synthesis. It is recently fount that in the absence of glycogen primer, a specific protein namely glycogenin can accept glucose from UDPG. The hydroxyl group of amino acid tyrosine of glycogenin is the site at which the initial glucose unit is attached. The…
The enzymes hexokinase in muscle and hexokinase in liver convert glucose to glucose 6-phosphate. Phosphoglucomutase catalyses the conversion of glucose 6-phosphate to glucose 1-phosphate. Uridine diphosphate glucose (UDPG) is synthesised from glucose 1-phosphate and UTP by UDP-glucose phosphorylase. Pyrophosphate (PPi) produced in this reaction is hydrolysed to inorganic phosphate, which will ensure the optimal synthesis of…