Transamination Reactions of Other Pyridoxal Phosphate Enzymes

5 Transamination Reactions of Other Pyridoxal Phosphate Enzymes Inaddition to theirmainreactions, anumberofpyridoxalphosphate-dependent enzymes also catalyze the half-reaction of transamination. Such enzymes include serine hydroxymethyltransferase (Section 10.3.1.1), several decarboxylases, and kynureninase (Section 8.3.3.2). 

The result of this half-transaminase reaction is formation of pyridoxamine phosphate at the active site of the enzyme, and hence loss of activity. Pyridoxamine phosphate dissociates from the active site, so that if adequate pyridoxal phosphate is available the resultant apoenzyme can be reactivated. 

The ratio of transamination decarboxylation is relatively small - of the order of 1 10,000 for glutamate decarboxylase. Nevertheless, this is sufficient to result in significant loss of active enzyme, andMeister (1990) suggested that this may be a control mechanism rather than simply a lack of reaction specificity. 

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