title: Substrate inhibition of transketolase.
abstract: We studied the influence of the acceptor substrate of transketolase on the activity of the enzyme in the presence of reductants. Ribose-5-phosphate in the presence of cyanoborohydride decreased the transketolase catalytic activity. The inhibition is caused by the loss of catalytic function of the coenzyme-thiamine diphosphate. Similar inhibitory effect was observed in the presence of NADPH. This could indicate its possible regulatory role not only towards transketolase, but also towards the pentose phosphate pathway of carbohydrate metabolism overall, taking into account the fact that it inhibits not only transketolase but also another enzyme of the pentose phosphate pathway--glucose 6-phosphate dehydrogenase [Eggleston L.V., Krebs H.A. Regulation of the pentose phosphate cycle, Biochem. J. 138 (1974) 425-435].
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia.
authors.forename: Olga N
authors.initials: ON
authors.lastname: Solovjeva
authors.affiliation: Department of Hepatopancreatobiliary and Regenerative Surgery, Sechenov First Moscow State Medical University, Ministry of Health of the Russian Federation, Trubetskaya Street 8/2, 119991 Moscow, Russia.
authors.forename: Marina V
authors.initials: MV
authors.lastname: Kovina
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia. Electronic address: kochetov@belozersky.msu.ru.
authors.forename: German A
authors.initials: GA
authors.lastname: Kochetov
mesh_terms: D001894:Borohydrides / Q000737:chemistry; D050260:Carbohydrate Metabolism; D008099:Liver / Q000737:chemistry / Q000201:enzymology; D009249:NADP / Q000737:chemistry; D010427:Pentose Phosphate Pathway; D019163:Reducing Agents / Q000737:chemistry; D012267:Ribosemonophosphates / Q000737:chemistry*; D012441:Saccharomyces cerevisiae; D013379:Substrate Specificity; D013835:Thiamine Pyrophosphate / Q000737:chemistry* / Q000378:metabolism; D014174:Transketolase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001894:Borohydrides; D019163:Reducing Agents; D012267:Ribosemonophosphates; C031626:ribose-5-phosphate; D009249:NADP; D014174:Transketolase; D013835:Thiamine Pyrophosphate
keywords: Pentose phosphate pathway; Reductants; Substrate inhibition; Thiamine diphosphate; Transketolase