Microsomal retinal synthesis: retinol vs. holo-CRBP as substrate and evaluation of NADP, NAD and NADPH as cofactors.
Holo-CRBP (cellular retinol binding protein) is recognized specifically by an NADP-dependent microsomal retinol dehydrogenase and protects retinol from conversion into retinal by NAD and NADPH dependent dehydrogenases. The synthesis of retinal from free retinol is catalyzed by both NADP- and NAD-dependent pathways, with the former being the preferred one (Km of 4 vs. 22 microM for retinol, and Vmax/Km of 33 vs. 9, respectively). NADPH does not support quantitatively significant retinal synthesis from physiological concentrations of retinol or holo-CRBP, if an NADPH regenerating system is used to prevent NADP formation.
Napoli
J L
JL
Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York Buffalo 14214.
Posch
K C
KC
Burns
R D
RD
D000818:Animals; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012172:Retinaldehyde / Q000096:biosynthesis*; D012177:Retinol-Binding Proteins / Q000378:metabolism*; D054840:Retinol-Binding Proteins, Cellular; D014801:Vitamin A / Q000378:metabolism
D011994:Recombinant Proteins; D012177:Retinol-Binding Proteins; D054840:Retinol-Binding Proteins, Cellular; D009243:NAD; D014801:Vitamin A; D009249:NADP; D012172:Retinaldehyde