Catalytic properties of NADPH-specific dihydropteridine reductase from bovine liver.
The catalytic properties of a new type of dihydropteridine reductase, NADPH-specific dihydropteridine reductase [EC 1.6.99.10], from bovine liver, were studied and compared with those of the previously characterized enzyme, NADH-specific dihydropteridine reductase [EC 1.6.99.7]. With quinonoid-dihydro-6-methylpterin, approximate Km values of NADPH-specific dihydropteridine reductase for NADPH and NADH were estimated to be 1.4 micron and 2,900 microns, respectively. The Vmax values were 1.34 mumol/min/mg with NADPH and 1.02 mumol/min/mg with NADPH. With NADPH, the Km values of the enzyme for the quinonoid-dihydro forms of 6-methylpterin and biopterin were 1.4 micron and 6.8 microns, respectively. The enzyme was inhibited by its reaction product, NADP+, in a competitive manner, and the inhibition constant was determined to be 3.2 microns. The enzyme was severely inhibited by L-thyroxine and by 2,6-dichlorophenolindophenol.
N
N
Nakanishi
H
H
Hasegawa
M
M
Akino
S
S
Yamada
D015086:2,6-Dichloroindophenol / Q000494:pharmacology; D000818:Animals; D002384:Catalysis; D002417:Cattle; D004093:Dihydropteridine Reductase / Q000032:analysis* / Q000037:antagonists & inhibitors; D006900:Hydroxylation; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009243:NAD / Q000494:pharmacology; D009247:NADH, NADPH Oxidoreductases / Q000032:analysis*; D009249:NADP / Q000378:metabolism* / Q000494:pharmacology; D010649:Phenylalanine / Q000378:metabolism; D013974:Thyroxine / Q000494:pharmacology
D009243:NAD; D010649:Phenylalanine; D009249:NADP; D015086:2,6-Dichloroindophenol; D004093:Dihydropteridine Reductase; D009247:NADH, NADPH Oxidoreductases; D013974:Thyroxine