Phosphorylation by Ca2+/calmodulin-dependent protein kinase II and protein kinase C of sepiapterin reductase, the terminal enzyme in the biosynthetic pathway of tetrahydrobiopterin.
Sepiapterin reductase, the terminal enzyme in the biosynthetic pathway of tetrahydrobiopterin, was stoichiometrically phosphorylated by Ca2+/calmodulin-dependent protein kinase II and protein kinase C (Ca2+/phospholipid-dependent protein kinase) in vitro. Maximal incorporation of phosphate into the enzyme subunit by these was 3.05 +/- 0.05 (n = 4) and 0.74 +/- 0.03 (n = 5) 32P mol per mol enzyme subunit, respectively. The enzyme was not phosphorylated by cyclic nucleotide-dependent protein kinase of either the cAMP-dependent or cGMP-dependent type in this study. Dihydropteridine reductase, another enzyme working in direct supply of tetrahydrobiopterin, was also a good substrate for Ca2+/calmodulin-dependent protein kinase II. Phosphorylation of sepiapterin reductase by these protein kinases modified the kinetic properties of the enzyme. It is likely that these multifunctional Ca(2+)-activated protein kinases may play a role in the regulation of the physiological function of the BH4-generating enzymes in vivo, as was previously found in the case of BH4-requiring enzymes.
Katoh
S
S
Department of Biochemistry, Meikai University School of Dentistry, Saitama, Japan.
Sueoka
T
T
Yamamoto
Y
Y
Takahashi
S Y
SY
D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives* / Q000096:biosynthesis; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D004093:Dihydropteridine Reductase / Q000378:metabolism; D004912:Erythrocytes / Q000201:enzymology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism
D001708:Biopterins; D000429:Alcohol Oxidoreductases; C022630:sepiapterin reductase; D013762:Tetrahydrofolate Dehydrogenase; D004093:Dihydropteridine Reductase; D011493:Protein Kinase C; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C003402:sapropterin