Reaction mechanism of gramicidin S synthetase 1, phenylalanine racemase, of Bacillus brevis.
We have demonstrated that gramicidin S synthetase 1 (GS 1), phenylalanine racemase [EC 5.1.1.11], of Bacillus brevis catalyzes the exchange between a proton in the medium and alpha-hydrogen of phenylalanine in the course of the racemase reaction by using tritiated water or L-phenyl[2,3-3H]alanine. GS 1 from some gramicidin S non-producing mutants of B. brevis lacking phenylalanine racemase activity did not catalyze the tritium exchange reaction. The proton exchange between phenylalanine bound as thioester on the GS 1-phenylalanine complex and water in the medium was detected, but 5,5'-dithiobis(2-nitrobenzoic acid)-modified complex lacked both the proton exchange and phenylalanine racemase activity. It is suggested that a base group, probably a sulfhydryl group, on the enzyme functions as proton donor and acceptor during the phenylalanine racemase reaction.
Department of Biochemistry, Hyogo College of Medicine.
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Kanda
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Hori
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Kurotsu
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Miura
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Saito
D000591:Amino Acid Isomerases / Q000302:isolation & purification / Q000378:metabolism*; D001407:Bacillus / Q000201:enzymology*; D004228:Dithionitrobenzoic Acid; D005415:Flavins / Q000032:analysis; D007202:Indicators and Reagents; D007536:Isomerism; D010649:Phenylalanine / Q000032:analysis; D011725:Pyridines / Q000032:analysis; D011732:Pyridoxal Phosphate / Q000032:analysis; D013438:Sulfhydryl Compounds / Q000032:analysis; D013997:Time Factors; D014316:Tritium; D014867:Water / Q000032:analysis
D005415:Flavins; D007202:Indicators and Reagents; D011725:Pyridines; D013438:Sulfhydryl Compounds; D014867:Water; D014316:Tritium; D010649:Phenylalanine; D011732:Pyridoxal Phosphate; D004228:Dithionitrobenzoic Acid; D000591:Amino Acid Isomerases; C022343:phenylalanine racemase (ATP-hydrolyzing)