Direct identification and quantification of the cofactor in glutamate semialdehyde aminotransferase from pea leaves

Glutamate semialdehyde aminotransferase, a key enzyme in the synthetic pathway leading to chlorophyll was purified from pea (Pisum sativum) leaves. Although the preparation contained a single contaminant the enzyme could be unambiguously identified as a dimer of subunit molar mass 45 kDa having an absorption spectrum consistent with the presence of pyridoxamine phosphate as cofactor. The cofactor was released by treatment with strong phosphate at low pH and was identified and quantified fluorimetrically. The specific activity of the enzyme (1.4 mumol.min-1.mg-1; 23 nkatal.mg-1) is very much higher than previously reported.