Open AccessThe Substrate Activation in Some Pyridine Nucleotide Linked Enzymic Reactions
Author(s) -
Watkinson Ian A.,
Wilton David C.,
Rahimtula Anver D.,
Akhtar M. Muhammad
Publication year - 1971
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1971.tb01583.x
Subject(s) - chemistry , protonation , desmosterol , substrate (aquarium) , double bond , nucleotide , stereochemistry , nad+ kinase , pyridine , hydride , photochemistry , hydrogen , medicinal chemistry , cholesterol , biochemistry , enzyme , ion , organic chemistry , gene , biology , ecology , sterol
The conversion of desmosterol into cholesterol was carried out in the presence of either tritiated water or [4 3 H 2 ]NADPH. The side chain fragment consisting of carbon atoms 23–27 of cholesterol was obtained through the combination of biological and chemical techniques. Selective degradation of the fragment led to the conclusion that in the saturation of the 24,25‐double bond of desmosterol a hydrogen atom from the medium is added to C‐24 and another from the 4‐position of NADPH to C‐25. These results in conjunction with similar studies previously reported on the saturation of other C═C in steroid biosynthesis are interpreted in terms of a general mechanism. It is suggested that the first crucial event in the pyridine nucleotide linked reduction is the activation of the substrate through protonation to give an electron deficient species which in the next step is neutralized by the addition of a hydride from NAD(P)H to furnish the product.