Pyridoxal 5′phosphate binding site of Escherichia Coli beta cystathionase and cystathionine gamma synthase comparison of their sequences

The phosphopyridoxyl peptides of β cystathionase and cystathionine γ synthase of Escherichia Coli were identified after reduction, carboxymethylation and proteolysis of the holoenzymes. Their comparison with those obtained from rat liver γ cystathionase (Fearon, C.W., Rodkey, J.A. and Abeles R.H. 1982. Biochemistry 21 3790 – 3794.) showed a high degree of homology between the three PLP binding sites with the presence of the tripeptide sequence: Thr-Lys(Pxy)-Tyr in their structure. This homology suggests that these enzymes of methionine metabolism have probably the same origin.