Co-Aminopherase, Co-Decar-Boxylase and Pyridoxal

Abstract

ARRANGEMENTS were made with Prof. Braunstein, as indicated, in his letter above, to carry out comparative assays of codecarboxylase, coaminopherase and barium-phosphopyridoxal preparations against aspar-tic-aminopherase on one hand and tyrosine decar-boxylase on the other: For assay of tyrosine codecarboxylase activity, tyrosine decarboxylase was prepared from S. fcecalis cells and the apo -enzyme made by precipitation with ammoniacal ammonium sulphate solution followed by standing at 0° as described by Epps16. We are indebted to Prof. I. C. Gunsalus for a sample of highly purified synthetic barium-phosphopyridoxal13, and a standard curve was obtained relating the activity of the tyrosine enzyme to the concentration of phosphopyridoxal. An amount of apo-enzyme preparation was chosen which would give 220 y.1. carbon dioxide from tyrosine in 5 min. at 30° and pH 5-5 when saturated with coenzyme; the corresponding value in the absence of added coenzyme was 4 [il./5 min. and the rate of carbon dioxide evolution bears a linear relation to phosphopyridoxal concentration for quantities of the latter up to 0-4|/gm. barium salt per 3 ml. (= 140 \ih carbon dioxide per 5 min.). For assay purposes amounts of the various cofactors were taken which would give rise to carbon dioxide evolution under the standard conditions of not more than 140 JJLL/5 min. and the equivalence of barium-phosphopyridoxal read off directly from the standard curve.