The indirect role of biotin in the synthesis of ornithine transcarbamyiase.

A number of years ago studies with bacteria indicated a role of biotin in the carboxylation reaction forming a 4 carbon unit essential for aspartate biosynthesis (1, 2). These studies led to extensive work on the role of biotin in the incorporation of bicarbonate into various metabolites. A role of biotin in transcarbamylase reactions was demonstrated when biotin-deficient cells of Streptococcus la&s 8039 and Lactobacillus arobinosus 1’7-5 were found to have appreciably less ornithine transcarbamylase and aspartate transcarbamylase than biotin-sufficient cells (3, 4). Ornithine transcarbamylase activity can be restored to biotindeficient cells of Streptococcus la&is upon incubation for a short period of time in the presence of biotin in an amino acid medium (5). However, acid hydrolysates of highly purified preparations of the enzyme do not contain significant amounts of biotin (6), and, therefore, the role of biotin appeared to be an indirect one associated with the synthesis of the enzyme. The lack of a biotin effect on the synthesis of carbamate kinase in Streptococcus la&is (7) eliminated the possibility of an effect resulting from decreased synthesis of the substrate, carbamyl phosphate. In the present investigation,’ an enzymatic digest of purified ornithine transcarbamylase was found to replace biotin in stimulating the production of the enzyme; however, enzymatic digests of casein are also effective. A study of the nature of the peptides replacing biotin indicated that derivatives of aspartic acid, particularly peptides of asparagine, replace biotin by supplying a source of 4 carbon units, the biosynthesis of which is dependent upon a carboxylation reaction involving biotin.