Studies of enzyme-mediated reactions. Part 13. Stereochemical course of the formation of histamine by decarboxylation of (2S)-histidine with enzymes from Clostridium welchii and Lactobacillus 30a

Abstract

(αS)-[α-³H]Histidine is prepared and the [α-³H₁]histamine produced from it by the decarboxylating enzymes of Clostridium welchii and Lactobacillus 30a is proved by assay with diamine oxidase from pea seedlings to have the (αS)-configuration. The (Si)-stereospecificity of the latter enzyme is confirmed for the case of histamine by studying its action on (αR)-[α-³H₁]histamine (21) which is synthesised rationally. The combined results prove that histidine decarboxylases from both sources bring about decarboxylation with overall retention of configuration. It is shown that histidine decarboxylase acts on histamine to bring about slow exchange with the medium of the α-Re-hydrogen, which occupies the same space (Re-space) as the carboxy-group of (αS)-histidine. Syntheses are described of (αS,βS)-[β-³H₁]histidine (45) and (αS,βR)-[β-³H₁]histidine (47).