α, β Elimination of β-Chloro-L-alanine and Syncatalytic Inactivation of α-Aminoisobutyrate Decomposing Enzyme

Abstract

β-Chloro-L-alanine was catalytically converted to pyruvate, ammonia and chloride by α-aminoisobutyrate (AIB) decomposing enzyme (α, β elimination), which was synchronously inactivated. There was a linear relationship between α, β elimination and inactivation. With apoenzyme, neither α, β elimination nor inactivation occurred. These facts suggest that α, β elimination is dependent on pyridoxal 5'-phosphate, and inactivation cooperates with α, β elimination (syncatalytic inactivation). But it seemed that D-form of β-chloroalanine was not a substrate for AM decomposing enzyme, because just half amount of β-chloro-DL-alanine was decomposed to pyruvate by the enzyme.
An identical active site for each of following three reactions were shown by the fact that AIB decomposing activity, transamination activity and α, β elimination activity were lost in parallel. From a kinetic study, the affinity of the enzyme toward β-chloro-L-alanine was shown to be higher than that toward AM or L-alanine. The turnover number, about 8, 000, of α, β elimination during the inactivation of one mol of the enzyme was much larger than that of n-amino acid transalninase or alanine racemase.