Page - (000057) - in Biomedical Chemistry: Current Trends and Developments

Scheme 1.1.41: Reaction scheme of the epimerisation of isopenicillin-N. Substitutions of the side chain can also be performed by penicillin acylase (PA) to give other types of penicillin. PA catalyses the hydrolysis and synthesis of the amide bond to some side chain. The use of this enzyme in vitro enables the formation of semi-synthetic penicillin. 1.1.5.4 NAD+ − a Classical Coenzyme An enzyme cannot catalyse oxidation reactions unless a coenzyme is present. In some sense, the enzyme’s role is to hold the substrate and coenzyme together to facilitate the oxidation reaction. One of the most commonly used coenzymes is nicotinamide adenine dinucleotide (NAD+) (Fig. 1.1.9). There is evidence that sirtuins are proteins related to several diseases and are NAD+ dependent. Figure 1.1.9: Structure of nicotinamide adenine dinucleotide (NAD+). The most known intervention of coenzyme NAD+ is its role in the ethanol metabolism, where it acts as a common hydride acceptor (Scheme 1.1.42).