Purification and characterisation of a microbial L-carnitine amidase

A novel enzyme, L-carnitine amidase, was purified about 140-fold from a newly screened microorganism (DSM 6320) to yield a homogeneous protein. The native enzyme has a molecular mass of 125 kDa (gel filtration) and consists of two identical subunits as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and Edman degradation. The pH optimum was found around pH 8.5. Out of 60 chemicals tested as substrates (amides of various aliphatic and aromatic acids, nitriles, amino acid amides and dipeptide amides) the amidase hydrolysed only L-carnitine amide. The Michaelis constant (Km) was found to be 11.6 mM, and the pure protein had a specific activity of 328 units/mg. Complex kinetics were observed with the racemic mixture of D,L-carnitine amide as starting material during enzymatic hydrolysis.