[2'-13C]Biotin was incorporated into avidin (egg white), glutaconyl-CoA decarboxylase (EC 4.1.1.70) from Acidaminococcus fermentans and the biotin carrier of transcarboxylase from Propionibacterium freudenreichii (EC 2.1.3.1). 13C-NMR measurements showed an upfield shift of the carbonyl carbon of 3.1 and 2.0 ppm for both enzymes, whereas binding to avidin induced no significant change of the chemical shift as compared to free biotin. The data indicate that the enzymes provide an electronic environment for the covalently bound biotin which favours carboxylation. In addition it was demonstrated by NMR-measurements that glutaconyl-CoA decarboxylase, from which the hydrophobic carboxy-lyase subunit (β) was removed, could carboxylate free biotin.
