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Coenzyme metabolism in rat liver transketolase

Journal Article · · Biochemistry (Engl. Transl.); (United States)
OSTI ID:5721633
On the basis of the results of kinetic investigations, two binding sites for hydroxythiamine diphosphate were determined in apotransketolase, with sharply differing values of K/sub i/: (7-22) x 10/sup -9/ and (13.0-19.7) x 10/sup -8/ M. A study was made of the turnover rate of thiamine diphosphate in holotransketolase in rat liver tissue by a radioisotope method, using (/sup 14/C) thiamine as the labeled precursor. The half-substitution time and rate constant of degradation of the coenzyme in transketolase are close in absolute values to the analogous indices for the protein portion of the enzyme and constitute 153 h and 0.108 day/sup -1/, respectively. Rat liver transketolase exists in vivo in the form of a substituted ..cap alpha..-carbanion. Replacement of thiamine diphosphate by hydroxythiamine diphosphate in the holoenzyme has no effect on the formation of the intermediate ..cap alpha..-carbanion form of the enzyme.
OSTI ID:
5721633
Journal Information:
Biochemistry (Engl. Transl.); (United States), Journal Name: Biochemistry (Engl. Transl.); (United States) Vol. 51:7; ISSN BIORA
Country of Publication:
United States
Language:
English