The pyridoxal- and pyridoxal 5′-phosphate-catalysed non-enzymic degradations of l-serine O-sulphate and related compounds

Abstract

1. l-Serine O-sulphate and l-threonine O-sulphate are degraded in the presence of pyridoxal 5′-phosphate to yield equimolar amounts of the corresponding keto acid, ammonia and sulphate. 2. Pyridoxal catalyses the same reactions at a faster rate. 3. One of a number of bi- or ter-valent metal ions must be present for these degradations to proceed. The reaction rates are dependent on a number of factors including pH and the nature of the metal ion used. 4. Studies with related sulphate esters indicate that the α-hydrogen atom and the amino group are essential for activity. 5. Spectral changes during the pyridoxal and pyridoxal 5′-phosphate catalysis of l-serine O-sulphate breakdown suggest the formation of a Schiff base. 6. The mechanism for these reactions appears to be in accordance with the general mechanism proposed for pyridoxal-catalysed αβ-elimination reactions.