Purification of Neurospora crassa cytosolic serine hydroxymethyltransferase.

Abstract

Serine hydroxymethyltransferase (SHMT) catalyzes the reversible interconversion of serine to glycine with tetrahydrofolate serving as a one-carbon acceptor (Reaction 1). This reaction is the major source of activated one-carbon groups required for the biosynthesis of purines, thymidylate, methionine, and choline. SHMT has been purified and characterized from many sources, including mammalian liver, prokaryotes, and several plant species.1,2,3,4,5 The mammalian and prokaryotic enzymes require pyridoxal phosphate as a cofactor, which exhibits specific absorption bands corresponding to different reaction intermediates. These absorption bands have been utilized in studies to determine both reaction specificity and the mechanism of the enzyme. The enzymes from rabbit liver and E. coli show very broad reaction specificity, catalyzing the cleavage of various 3-hydroxy amino acids, the transamination of D and L-alanine, and the decarboxylation of aminomalonate.1,2 SHMT is present in both the cytosol and mitochondria of eukaryotes, however the isozymes have been separately purified only from rat and rabbit liver. The isozymes from these two sources appear to exhibit the same spectral and catalytic properties.1 SHMT has also been purified from several plant species. These enzymes also have a pyridoxal phosphate bound to the active site of the purified enzyme. However, it has been reported that the enzyme from mung bean is not a pyridoxal phosphate dependent enzyme.5 KeywordsAmmonium SulfatePotassium PhosphateNeurospora CrassaEquilibration BufferRabbit LiverThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.