Manometric assay and cofactor requirements for serine hydroxymethylase.

The enzymatic conversion of serine to glycine and the reverse process have been shown to occur in a variety of avian (l-7), mammalian (8-16), and bacterial (17-20) tissues or tissue extracts. In almost all instances, sensitive tracer techniques, with C14or N16-labeled substrates, have made it possible to study the reaction even though, in many instances, the net conversions were small. It has been indicated from these investigations that the p-carbon atom of serine is released as a coenzyme-bound Cl unit’ at the oxidation level of formaldehyde. In various systems, tetrahydrofolic acid (FHJ, or a derivative of FH4, Mn++ ions, pyridoxal phosphate, diphosphopyridine nucleotide (DPN) and triphosphopyridine nucleotide (TPN) have been implicated as cofactors for the reaction. The present communication describes the preparation from beef liver of a soluble enzyme system, serine hydroxymethylase, which converts serine to glycine. The C1 unit is oxidized in two steps to COZ, thus enabling the over-all reaction to be followed conveniently in manometers. The requirement for various cofactors in this system makes it possible to discuss the reaction mechanism, and provides information of value for the subsequent fractionation and study of individual enzymatic components of the overall system.