Serine Transhydroxymethylase from Rabbit Liver

Abstract
The amino acid sequence of′ the coenzyme‐binding site of serine transhydroxymethylase from rabbit liver has been determined. After reduction with NaBi14 and aminoethylation, a first sample of enzyme was digested with thermolysin and a single phosphopyridoxyl peptide was isolated.A second sample of similarly treated enzyme was digested with chymotrypsin and three phosphopyridoxyl peptides clearly originating from a unique coenzyme‐binding site were isolated. Sequence analysis of these peptides indicate the following structure: Val‐Val‐Thr‐Thr‐Thr‐His‐Lys (Pxy) ‐Thr‐Leu. Sequence homologies of the active site of various pyridoxalphosphate enzymes are discussed in terms of a possible catalytic role and of evolution of this class of proteins.