Serine Transhydroxymethylase of Cauliflower (Brassica oleracea var. botrytis L.): Partial Purification and Properties.

Serine transhydroxymethylase (EC 2.1.2.1) has been purified 46-fold from cauliflower (Brassica oleracea var. botrytis L.). The enzyme was completely dependent on the presence of tetrahydrofolic acid for the conversion of serine to glycine. The addition of pyridoxal phosphate gave a large increase in the reaction rate. A double pH optimum was observed with maxima at 7.5 and 9.5. The enzyme is specific for l-serine. The d-isomer is neither a substrate nor an inhibitor. The Michaelis constants for l-serine, tetrahydrofolic acid, and pyridoxal phosphate were 300 mum, 760 mum, and 24 mum, respectively. The addition of K(+) also stimulated the reaction rate considerably. The effect was quite specific since all other metal ions tested either had very little: influence or were extremely inhibitory.