Biochemistry of the evolution of Triatoma infestans. XII. Biosynthesis and secretion of a very high density lipoprotein.

Biosynthetic processes related to the production of an insect hexamerin, very high density lipoprotein (VHDL), have been examined in the fat body of fifth-instar nymph and adult Triatoma infestans. Fat bodies were incubated in vitro with [3H]leucine and the incubation media were precipitated using a specific antiserum. The SDS-polyacrylamide gel electrophoresis followed by blotting on nitrocellulose showed that both larval and adult fat body secreted the VHDL subunit. Moreover, the radiolabel recovered in this subunit is indicative of the de novo synthesis. When the incubation medium was subjected to density gradient ultracentrifugation, a radiolabeled fraction was found at density 1.27 g/ml, value identical to the hemolymph circulating VHDL, indicating that the secreted apoprotein is combined with lipids. The SDS-polyacrylamide gel electrophoresis and immunoblotting of this fraction corroborated the presence of the VHDL-apoprotein. These results demonstrate that the fat body of T. infestans is able to synthesize the protein subunit which is associated to lipids as a lipoprotein particle that is released into the medium as VHDL.