Lipoprotein transformations during adipokinetic hormone action in Locusta migratoria

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Abstract
Detailed studies of lipoprotein A+ formation during AKH action have been made in Locusta migratoria L. using gel filtration combined with the use of radiolabeled haemolymph protein probes. In addition, we have assessed the quantitative contribution of the CL‐proteins to A+ formation by direct measurement of the changes in concentration of free CL‐proteins and report some properties of the C‐I and C‐II proteins: they appear to be glycoproteins of 20,000 and 16,000 MW respectively, but do not bind to concanavalin A. We have confirmed earlier observations (using different techniques) which showed that liproprotein Ayellow is not involved per se in A+ formation during the first 15 min of AKH action. In contrast, the (two) CL‐proteins take part in A+ formation without any apparent delay after hormone injection. Our observations show that A+ formation is essentially complete within 30 min of AKH injection, although further CL‐protein binding and lipid‐loading do occur subsequently. After 30 min there is no further decrease in the Ayellow titre. It is argued that much, if not all, CL‐protein is located at the surface of the A+ particle. From the changes in titres which occur in Ayellow and CL‐proteins during AKH action we estimate that A+ is formed from 1 mole of Ayellow and approximately 28 moles of CL‐proteins. Using these figures we calculate an apparent molecular weight for A+ within the range of 1.65–2.12×106, which is in reasonable agreement with estimates derived from gel exclusion chromatography data. These studies emphasize the dynamic and fully reversible nature of lipoprotein A+ formation and highlight the complex nature of the lipoprotein transformations occurring during hormone‐stimulated lipid transport in locusts.