Lipid transfer particle in the hemolymph of the American cockroach: evidence for its capacity to transfer hydrocarbons between lipophorin particles.

Abstract

A lipid transfer particle (LTP) was isolated and purified from the hemolymph of the adult male American cockroach, Periplaneta americana, essentially according to the method previously developed for the purification of LTP from locust hemolymph. Fast protein liquid chromatography (FPLC) on a Mono Q column was used as the additional step to obtain pure LTP. The electron micrograph of purified cockroach LTP exhibited an unusual and asymmetric shape essentially similar to that reported for Manduca sexta LTP (Ryan et al. 1990. J. Lipid Res. 31:871-879). The cockroach LTP was also found to be basically similar to that of M. sexta and locust in terms of subunit structure and lipid composition, although there were significant differences particularly in the contents of hydrocarbons and diacylglycerol. A simple method for assaying LTP activity was developed, based on the finding that cockroach LTP can catalyze the transfer of labeled hydrocarbons (or diacylglycerol) from labeled high density lipophorin (HDLp) bound with a transfer membrane (Immoblion) to unlabeled HDLp dissolved in saline. This finding reveals that cockroach LTP has the capacity to transfer and/or exchange lipids between lipophorin particles with the same density. It was also demonstrated that cockroach LTP has the capacity to catalyze the transfer and/or exchange of hydrocarbons, in addition to diacylglycerol, between cockroach HDLp and locust low density lipophorin (LDLp).