Studies on the enzymic reduction of amino acids: a proline reductase of an amino acid-fermenting clostridium, strain HF

Abstract

The proline-reductase system of a clostridium, strain HF, catalyses the quantitative reduction of DL-proline to [delta]-amino-valeric acid. In unfractionated extracts, a number of thiols serve as reducing agents for the process. Certain dithiols structurally related to 6:8-dithioloctanoic acid (lipoic or thioctic acid) are most active. The cofactors necessary for maximum proline reduction in the isolated system are diphosphopyridine nucleotide (DPN), Mg2+ and pyridoxal phosphate. The enzymes responsible for reduction were partially purified by ammonium sulfate precipitation. Ability of a number of the thiols to serve as reducing agents is lost during purification of the enzyme system. Although the preparations contain a DPN-linked dithiol dehydrogenase, reduced DPN neither replaces the dithiol nor supplements it at rate-limiting concentrations in the proline-reductase system. [DELTA]-Pyrroline-5-carboxylic acid is not a free intermediate in the reduction of proline to [delta]-aminovaleric acid.