Pyridoxal phosphate as a constituent of the histaminase (benzylamine oxidase) of pig plasma

Abstract

The histaminase (‘benzylamine oxidase’) of pig plasma has recently been crystallized and a description is given of some of the physical and chemical properties of the pure preparation of the oxidase. The fluorescence of the enzyme is typical of a protein containing tryptophan. The phosphorus content is about four atoms per molecule. On enzymic hydrolysis a product has been obtained that has the fluorescence properties of a pyridoxal protein. This product gave rise on acid hydrolysis to material capable of activating the L-tyrosine apodecarboxylase of Streptococcus faecalis R in the presence of adenosine triphosphate, indicating that pyridoxal was set free in the hydrolysis. Acid hydrolysis of a solution of the crystalline enzyme and subsequent treatment with urea yielded diffusible material with the spectroscopic and fluorescence properties of pyridoxal. Using the bacterial apodecarboxylase, traces of pyridoxal phosphate and larger amounts of free pyridoxal were shown to be present. It was calculated that about 3 or 4 moles of pyridoxal were present per mole of enzyme. Together with the phosphate estimations, these observations lead to the conclusion that the oxidase contains 3 or 4 moles of pyridoxal phosphate per mole. Observations on rats maintained on a diet deficient in vitamin B 6 are in agreement with these conclusions.