Fatty acid synthetases from Euglena gracilis. Separation of component activities of the ACP-dependent fatty acid synthetase and partial purification of the beta-ketoacyl-ACP synthetase.

The component enzymes of the chloroplast-associated, acyl carrier protein (ACP)-dependent, fatty acid synthetase (FAS-11) from Euglena gracilis have been independently examined by gel filtration chromatography of crude extracts from photoautotrophic cells. The acetyl coenzyme A:ACP transacylase, malonyl CoA:ACP transacylase, and /3-ketoacyl-ACP reductase activities were clearly resolved with apparent molecular weights of 147,000,106,000, and 44,000, respectively. The fl-ketoacyl-ACP synthetase, fl-hydroxyacyl-ACP dehydrase, and enoyl-ACP reductase activities in crude extracts migrated in an unresolved peak with an apparent molecular weight of 280,000. FAS-I1 activity, which exhibited an apparent molecular weight of 173,000, resulted f rom the overlapping portions of the six component activities. Under certain conditions, several of the E. gracilis FAS-I1 component activities may aggregate noncovalently to form a weak complex. A partial purification of t h e /3-ketoacyl-ACP synthetase by ammonium sulfate fractionation, DEAE-cellulose chromatography, and hydroxylapat i te chromatography resulted in its complete separation from the enoyl-ACP reductase activity. A portion of the enoyl-ACP reductase activity co-purified with the fl-ketoacyj-ACP synthetase activity through the DEAE-cellulose chromatography. When the separated /3-ketoacyl-ACP synthetase and enoylACP reductase activities were recombined and subjected to gel fi l tration chromatography, the two activities migrated distinctly and with lower apparent molecular weights, 118,000 and 56,500, respectively, than when similarly measured in the crude extract.