LYSOPHOSPHATIDIC ACID ACYLTRANSFERASE FROM IMMATURE COCONUT ENDOSPERM HAVING MEDIUM-CHAIN LENGTH SUBSTRATE-SPECIFICITY

Immature endosperm of coconut (Cocos nucifera) contains a membrane-bound lysophosphatidic acid acyltransferase (LPAAT) having medium chain length substrate specificity appropriate to the biosynthesis of coconut oil. Acyl-CoAs containing 10:0, 12:0 and 14:0 acyl groups are the preferred acyl-donor substrates; acyl-ACPs are not utilized. There is slight preference for 12:0-lysophosphatidic acid (LPA) over 18:1-LPA as acceptor substrate. Treatment of the active membrane fraction with 2.25% (w/v) CHAPS, at a detergent:protein ratio of 48:1 (w/w), in the presence of 1M NaCl solubilized the enzyme in high yield. Solubilization was evidenced by three independent criteria, namely, failure of the activity to sediment at high centrifugal force, behaviour of the activity as a globular protein of apparent M(r) 44000 in size-exclusion chromatography, and partial resolution of the activity from many of the membrane proteins on the size-exclusion column. Optimal restoration of LPAAT activity after solubilization required the addition of detergent-treated phospholipids, in addition to a lowering of the detergent and NaCl concentrations.