Comparative studies on threonine and serine dehydratases in rat liver.

1. Two isoenzymes of serine (threonine) dehydratase can be separated by DEAE cellulose chromatography. 2. Each of these isoenzymes possesses different S:T (serine dehydratase activity: threonine dehydratase activity) ratio and kinetic properties. 3. In early postnatal development, the S:T ratio shows marked variation. 4. The hepatic S:T ratio also changes with dietary manipulations. Furthermore L-alanine inhibits enzymic activities towards serine and threonine to different extent. 5. The results are consistent with the hypothesis postulating the presence of two distinct proteins each having a different activity ratio towards serine and threonine.