N-l -Carboxybiocytin

Carboxybiotin. The structure of biotin suggested that bicarbonate might be incorporated reversibly into its position 2. However, this proved not to be true and it remained for F. Lynen and associates to obtain a clue from a "model reaction." They showed that purified P-methylcrotonyl-CoA carboxylase promoted the carboxylation of free biotin with bicarbonate (H14C03 ) and ATP. While the carboxylated biotin was labile, treatment with diazomethane (Eq. 14-6) gave a stable dimethyl ester of N-l -carboxybiotin.53 54 The covalently bound biotin at active sites of enzymes was also successfully labeled with 14C02 Treatment of the labeled enzymes with diazomethane followed by hydrolysis with trypsin and pepsin gave authentic N-l -carboxybiocytin. It was now clear that the cleavage of ATP is required to couple the C02 from HCOs to the biotin to form carboxybiotin. The enzyme must... 

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