LIPID TRANSFER PARTICLE IN THE HEMOLYMPH OF THE AMERICAN COCKROACH - EVIDENCE FOR ITS CAPACITY TO TRANSFER HYDROCARBONS BETWEEN LIPOPHORIN PARTICLES

A lipid transfer particle (LTP) was isolated and purified from the hem olymph of the adult male American cockroach, Periplaneta americana, es sentially according to the method previously developed for the purific ation of LTP from locust hemolymph. Fast protein liquid chromatography (FPLC) on a Mono Q column was used as the additional step to obtain p ure LTP. The electron micrograph of purified cockroach LTP exhibited a n unusual and asymmetric shape essentially similar to that reported fo r 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. se xta and locust in terms of subunit structure and lipid composition, al though 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 ca talyze the transfer of labeled hydrocarbons (or diacylglycerol) from l abeled 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 lipid s between lipophorin particles with the same density. It was also demo nstrated that cockroach LTP has the capacity to catalyze the transfer and/or exchange of hydrocarbons, in addition to diacylglycerol, betwee n cockroach HDLp and locust low density lipophorin (LDLp).