ç-Glutamyl transpeptidase of the ackee plant

ABSTRACT

The enzyme ç-glutamyl transpeptidase was purified from seeds of immature ackee fruit (Blighia sapida; Sapindaceae) by salt fractionation and gel filtration on Biogel P-10 and P-200. The procedure, which differs from an an earlier one applied to kidney bean fruit, achieves 9.8 percent yield and 577-fold purification. The enzyme is also present in other parts of the fruit and in leaves. A MW of 12 500 was found by SDS-polyacrylamide gel electrophoresis, a value much lower than that reported for the enzyme from kidney bean fruit. Neutral or amino sugar accounts for 10 percent of the dry weight. In vitro, the enzyme catalysed synthesis of an unusual ç-glutamyl dipeptide which occurs in ackee seeds, using glutathione as glutamyl group donor. The enzyme mechanism was of the double displacement (ping-pong) type. (AU)