THE INTERACTION OF GLUTAMATE-DECARBOXYLASE FROM ESCHERICHIA-COLI WITHSUBSTRATE-ANALOGS MODIFIED AT C-3 AND C-4

The interaction of glutamate decarboxylase with the aspartate analogue s 3-arsonoalanine and 3-phosphonoalanine, with the glutamate analogues 2-amino-4-arsonobutyric acid and 2-amino-4-phosphonobutyric acid, and with 4-(methylthio)-L-glutamic acid, both as a mixture of diastereois omers and as the (2S,4R)-form, was studied. All these analogues were p oor substrates for the enzyme and only weak inhibitors. Their decarbox ylation was accompanied by transamination of the enzyme-bound pyridoxa l phosphate (PLP) to pyridoxamine phosphate (PMP), thus inactivating t he decarboxylase. With arsonoalanine only part of the PLP was converte d into PMP.