Enzymatic and mechanistic studies on the formation of N-phenylglycolohydroxamic acid from nitrosobenzene and pyruvate in spinach leaf homogenate.
The biotransformation mechanism of an unknown metabolite formed enzymatically from nitrosobenzene (NOB) and pyruvate in spinach (Spinacea oleracea L.) was investigated using spinach leaf homogenate. The unknown metabolite was identified as N-phenylglycolohydroxamic acid (PGA). The activity of PGA formation was decreased by l-alanine, increased by l-serine, and completely inhibited by aminooxyacetic acid, an inhibitor of transaminases. These results indicate that the transaminase participates in PGA formation. Indeed, hydroxypyruvate and alanine were produced in the transamination between pyruvate and serine. Hydroxypyruvate served as a direct-acting glycoloyl donor for PGA formation. A good correlation between the activities of the 200 g supernatant of spinach homogenate and commercial yeast transketolase for PGA formation from several glycoloyl donors was obtained. These results suggest the following mechanism for PGA formation from NOB and pyruvate: transamination of l-serine into hydroxypyruvate, which serves as a glycoloyl donor to NOB.
Tatsunami
Ryosuke
R
Department of Pharmacy, Hokkaido Pharmaceutical University School of Pharmacy, 7-1 Katsuraoka-cho, Otaru, Hokkaido 047-0264, Japan.
Yoshioka
Tadao
T
D000596:Amino Acids / Q000494:pharmacology*; D006877:Hydroxamic Acids / Q000378:metabolism*; D007700:Kinetics; D009603:Nitroso Compounds / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology; D019289:Pyruvic Acid / Q000378:metabolism*; D018724:Spinacia oleracea / Q000201:enzymology*; D000637:Transaminases / Q000378:metabolism*; D014174:Transketolase / Q000378:metabolism
D000596:Amino Acids; D006877:Hydroxamic Acids; D009603:Nitroso Compounds; C015437:N-phenylglycolhydroxamate; D019289:Pyruvic Acid; D014174:Transketolase; D000637:Transaminases; C012456:nitrosobenzene