ARGININE DECARBOXYLASE OF OAT SEEDLINGS

Arginine decarboxylase activity in the shoots of seedlings was high in oats, intermediate in barley and low in rice, maize, wheat and rye. After partial purification, the arginine decarboxylase from the shoots of potassium deficient oat seedlings was separated into two fractions, A (MW 195 000) and B (MW 118 000), by gel chromatography. On gel electrophoresis, the mobilities of these fractions were respectively 0.12 and 0.55 relative to bromophenol blue at pH 9.5. Fraction A was twice as active as fraction B in extracts of seedlings grown with both normal and potassium deficient nutrition, despite the greater activity ( × 5) of the potassium deficient plants. The properties of the two fractions were similar with respect to pH optimum (7-7.5), Km (3 × 10 -5M) and the effect of inhibitors. Fraction A was purified to apparent homogeneity by DEAE-cellulose chromatography. The enzyme was specific for l-arginine and it was strongly inhibited by NSD 1055, d-arginine and canavanine. Mercaptoethanol and dithiothreitol stimulated the enzyme by ca 50% and p-chloromercuribenzoate was an inhibitor. Pyridoxal phosphate stimulated activity by ca 30% and EDTA stimulated activity by 30%. Ca2+ and Mg2+ inhibited the enzyme by 50% at ca 20 mM. Putrescine and the polyamines showed only moderate inhibition at 10 mM, but agmatine reduced activity to 30% at this concentration. © 1979.