Serine Transhydroxymethylase

Abstract

Abstract A modified method for the purification of serine transhydroxymethylase from rabbit liver is presented. The purified enzyme is not only shown to catalyze the cleavage of serine but in addition, the cleavage of l-threonine and dl-allothreonine to glycine and acetaldehyde. The last two reactions had previously been thought to have been catalyzed by two separate enzymes, i.e. threonine aldolase and allothreonine aldolase. The evidence in support of a single enzyme catalyzing the three reactions includes the constant ratio for the specific activities during purification, similarity in affinity constants for substrates and inhibitors, and the ability of d-alanine to remove pyridoxal phosphate from the active site by transamination for both the allothreonine and serine reactions.