Kinetics of biotinyl-5'-adenylate synthesis catalyzed by the Escherichia coli repressor of biotin biosynthesis and the stability of the enzyme-product complex

Purification and characterization of intact and truncated forms of the Escherichia coli biotin carboxyl carrier subunit of acetyl-CoA carboxylase

Biotin biosynthesis and retention in Escherichia coli is regulated by the multifunctional protein, BirA. The protein acts as both the transcriptional repressor of the biotin biosynthetic operon and as a ligase for covalent attachment of biotin to a unique lysine residue of the acetyl-CoA carboxylase. Biotinyl-5'-AMP is the activated intermediate for the ligase reaction and the allosteric effector for DNA binding. We have purified and characterized apoBCCP and a truncated form containing the COOH-terminal 87 residues (apoBCCP87). Molecular masses of the proteins measured using matrix-assisted laser desorption ionization time-of-flight mass spectrometry conformed to the expected values. The assembly states of apoBCCP and apoBCCP87 were determined using sedimentation equilibrium ultracentrifugation. Nearly quantitative enzymatic transfer of biotin from BirA-biotinyl-5'-AMP to the apoBCCP forms was assessed using two methods, mass spectrometric analysis of acceptor proteins after incubation with BirA-bio-5'-AMP and a steady state fluorescence assay. The BirA catalyzed rates of transfer of biotin from bio-5'-AMP to apoBCCP and apoBCCP87 were measured by stopped-flow fluorescence. Kinetic parameters estimated from these measurements indicate that the intact and truncated forms of the acceptor protein are functionally identical.

Protein biotinylation in higher plants: characterization of biotin holocarboxylase synthetase activity from pea (Pisum sativum) leaves

Biotin holocarboxylase synthetase was partially purified from pea leaves by a sequence of ammonium sulphate fractionation and DEAE 52-cellulose chromatography. Enzyme activity was assayed using apo-(biotin carboxyl carrier protein) from an Escherichia coli bir A mutant affected in biotin holocarboxylase synthetase activity. Conditions for optimal catalytic activity and biochemical parameters of the plant enzyme were determined. This is the first direct evidence of the existence of biotin holocarboxylase synthetase activity in plants.