DEPLETION AND REPLETION OF BIOTINYL ENZYMES IN LIVER OF BIOTIN-DEFICIENT RATS - EVIDENCE OF A BIOTIN STORAGE-SYSTEM

The quantities of biotinyl proteins in liver of young rats were compar ed with age-matched controls at intervals during depletion and repleti on of biotin. Growth rate and the concentrations of biotinyl proteins previously proposed as mitochondrial storage forms of acetyl CoA carbo xylase rapidly decreased in response to biotin deprivation, whereas ne ither the concentration nor activity of cytosolic acetyl CoA carboxyla se was affected. Concentrations of carboxylases active within mitochon dria (pyruvate carboxylase, propionyl CoA carboxylase and 3-methyl cro tonyl CoA carboxylase) decreased only after d 28. When biotin was inje cted into biotin-deficient rats, concentrations of the carboxylases ac tive within mitochondria were restored to control levels within 3 h, w hereas the concentrations of putative mitochondrial storage forms of a cetyl CoA carboxylase reached normal levels only after 9 h, indicating that the injected biotin was preferentially used for the synthesis of the carboxylases active within mitochondria rather than acetyl CoA ca rboxylase. Mitochondrial acetyl CoA carboxylase may serve as a reservo ir to maintain a normal concentration of cytosolic acetyl CoA carboxyl ase in liver of rats deprived of biotin and provide biotin, indirectly , to maintain essentially normal concentrations of the biotinyl enzyme s active within mitochondria for several weeks after rats were fed a b iotin-deficient diet.