Biotinyl transferase activity

In addition to its hydrolase activity with maximal velocity at acidic pH, biotinidase also possesses biotinyl-transferase activity at physiological pH, resulting in the biotinylation of nucleophilic compounds such as histones [13]. This activity may play an important role in the regulation of gene expression [30]. Both hydrolase and transferase activities are affected in patients with biotinidase deficiency [13]. 

Hymes J, Fleischhauer K, Wolf (1995) Biotinylation of histones by human serum biotinidase assessment of biotinyl-transferase activity in sera from normal individuals and children with biotinidase deficiency. Biochem Mol Med 56 76-83... 

Bound biotin is recovered as free biotin in animals after proteolysis of biotin-dependent enzymes (from endogeneous tiolocarboxylases and during digestion), leading to biocytin (biotinyl-5 -lysine), which in turn is hydrolyzed to lysine and biotin by biotinidase. Biotinidase (37) has been extensively studied (cloned and purified) because it is related to biotin deficiency in human and numerous assays for biotinidase activity have been designed (38,39). It has been shown that biotinidase also supports biotinyl transferase activity and that this may actually be the main catalytic function for this enzyme, particularly in neuronal cells (40). 

In 1995, Hymes and Wolf discovered that biotini-dase can act as a biotinyl-transferase biocytin serves as the source of biotin, and histones are specifically biotinylated. Approximately 25% of total cellular biotinidase activity occurs in the nucleus. Zempleni and coworkers demonstrated that the abundance of biotinylated histones varies with the cell cycle, that biotinylated histones are increased approximately twofold compared to quiescent lymphocytes, and that histones are debiotinylated enzymatically in a process that is at least partially catalyzed by biotinidase. These observations suggest that biotin plays a role in regulating DNA transcription and regulation. 

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