Isolated apolipophorin III from Galleria mellonella stimulates the immune reactions of this insect

Apolipophorin III (apoLp-III) was isolated from the haemolymph of last instar larvae of Galleria mellonella. The ultraviolet (u.v.) spectrum and the N-terminal amino acid sequence reveal high similarities with the apoLp-III from Manduca sexta, The protein is heat-stable, The molecular mass of apoLp-III was determined to be 18 077 Da using mass spectrometry, The heat treatment (90 degrees C, 30 min) resulted in a pI shift from 6.6 for the non-heated to 6.1 for the heat-treated apoLp-III without change in the molecular mass, indicating that a conformational change might have been caused by the heat treatment, rather than covalent alterations, Intrahaemocoelic injection of pure apoLp-III into last instar G. mellonella larvae is followed by a dose-dependent increase of antibacterial activity in cell-free haemolymph of treated larvae 24 h after injection, Furthermore, pure apoLp-III enhances the phagocytic activity of isolated haemocytes in vitro, Tbe newly discovered role of apoLp-III in inducing immune-related functions in insects is discussed in regard to the known features.-of this molecule in lipid metabolism, Arylphorin, another heat-stable protein in G. mellonella haemolymph, was likewise isolated in this study, The protein was identified by N-terminal protein sequencing, the sequence obtained exactly matches the known sequence data for this protein. (C) 1997 Elsevier Science Ltd.