Page - (000049) - in Biomedical Chemistry: Current Trends and Developments

isomerase enzymes, through a cysteine residue, are responsible for this isomerization. The next step is Schiff base (imine) formation through the reaction of retinal with a lysine residue of the protein opsin to produce rhodopsin, which isomerizes upon absorption of visible light. This change in geometry causes an electrical signal that is sent to the brain. Finally, the hydrolysis of the imine linkage regenerates the opsin protein and (11E)-retinal (Scheme 1.1.36). Scheme 1.1.36: The chemistry of vision. 1.1.5.2 Metabolism of Fatty Acids ‒ β-Oxidation Pathway The catabolism of fatty acids (saturated or unsaturated) starts with chemical activation by esterification with coenzyme A (Scheme 1.1.37), with the following steps occurring in an acyl-CoA synthase: 1. The carboxylate acts as a nucleophile to attack the double P‒O bond in ATP;