Lipolytic activity in the flight muscles of Locusta migratoria measured with haemolymph lipoproteins as substrates

Abstract

A radiochemical assay is described in which neutral lipids presented as part of authentic haemolymph lipoproteins have been used as substrates to measure the lipolytic activity in the flight muscles of Locusta migratoria. The radiolabel in the substrate was located almost exclusively in the glycerol backbone of long chain acylglycerols (predominantly diacylglycerols) and the release of radiolabelled glycerol during incubation with muscle homogenates must therefore be due to “true” lipase activity rather than non-specific esterases. As the diacylglycerols were lipoprotein-bound, such enzymes may be regarded as lipoprotein lipases and this work therefore provides the first direct evidence for the existence of this group of enzymes in an insect tissue. Lipolytic activity in flight muscles has a single pH optimum with a peak at 7.5–8.0 and is only partially inhibited by 1 M NaCl which suggests dissimilarity with mammalian lipoprotein lipase. The activity and characteristics of the locust enzyme are discussed in relation to the energy requirements of flying locusts and in relation to what is known of the vertebrate enzyme.