Thomas K.F. Schulz

Adipokinetic hormone-induced lipid mobilization and lipophorin interconversions in fifth larval instar locusts

Abstract The response of fifth larval instar locusts to injected adipokinetic hormone (AKH) is only poor, as is reflected in both a very moderate elevation of the haemolymph lipid concentration and the slight occurrence of the haemolymph lipophorin interconversions characteristic for adult locusts, resulting in formation of only small quantities of the low density lipophorin (A + ). However, an additional lipophorin fraction (A′) is induced, which is intermediate in density and size between high and low density lipophorin and which is not identified in adult haemolymph. As in adults, larval A + formation includes association of the resting high density lipophorin with a non-lipid containing protein (C 2 ), the haemolymph concentration of which is only one-fifth relative to adults. However, the larval haemolymph protein composition is not the primary cause of the incomplete adipokinetic response, as elevation of the concentration of protein C 2 by injection of isolated adult C 2 , whether or not in combination with adult high density lipophorin, did not increase lipophorin conversions nor haemolymph lipid elevation. In vitro incubation of larval fat bodies in adult haemolymph showed that competency to both the AKH-induced lipid release and the haemolymph lipophorin conversions of the larval fat body are reduced compared to equal amounts of adult tissue. Reciprocal incubation of adult fat body in larval haemolymph resulted in only a very moderate adipokinetic response, demonstrating that larval haemolymph protein composition is restrictive for full development of hormone action. Both immunoblotting experiments and enzyme-linked immunosorbent assays (ELISA), using monoclonal antibodies specific for the adult lipophorin apoproteins, indicated that the larval lipophorins closely resemble the adult forms. Apparently the structure of locust lipophorins is remarkably constant throughout development despite changes in metabolic functions.

In vitro production of propionate by mantle mitochondria of the sea mussel Mytilus edulis L.: Overall mechanism☆

Abstract 1. 1. In this study it is demonstrated that mantle mitochondria of Mytilus edulis L. possess the enzyme system to convert succinate into propionate. 2. 2. The in vitro propionate synthesis is optimal at a succinate concentration of about 16 mM at pH 6.7. ADP, inorganic phosphate and Mg 2+ are required while relative low concentrations of malate markedly enhance the formation of propionate. 3. 3. It is suggested that malate provides succinyl-CoA through 2-oxoglutarate and thus sparks the synthesis of propionate.

In Vitro Biosynthesis of Locust Adipokinetic Hormones: Isolation and Identification of the Bioactive Peptides and Their Prohormones

The biosynthesis of adipokinetic hormones (AKH) I and II and their precursors was studied in the migratory locust Locusta migratoria using radiolabeled amino acids in an in vitro system. The peptides from the glandular part of the corpora cardiaca (CC) were extracted and separated by reversed-phase high performance liquid chromatography (HPLC). Incorporation of the [3H] amino acids was measured by monitoring the radioactivity of the column eluate. Total time for biosynthesis and processing of the prohormones to the bioactive AKH I and II was 75 min. Only the glandular part of the CC synthesized these peptide hormones.

Lipophorin conversions during flight of the death's-head hawkmoth Acherontia atropos

Abstract Flight activity or injection of the deaths-head hawkmoth Acherontia atropos with locust synthetic adipokinetic hormone (AKH I) results in a dramatic increase in the concentration of hemolymph diacylglycerol which is carried by specific lipophorins. In resting hawkmoths diacylglycerols are associated with a high-density lipophorin (HDLp, density ∼1.13 g/ml) consisting of two major apolipophorins (apoLp-I and -II, mol. wt ∼240,000 and 70,000, respectively). During flight or after AKH injection the formation of a new low-density lipophorin is induced (LDLp, density ∼1.03 g/ml), exhibiting a much higher lipid loading and consisting of HDLp subunits and an additional subunit (apoLp-III, mol. wt approx. 20,000). This subunit is a regular constitutent of hemolymph proteins in resting hawkmoths and consists of two protein components with slightly different molecular weights. The component with the lowest molecular weight seems to be preferentially incorporated into the newly generated LDLp. In the resting situation the HDLp already contains some apoLp-III. In spite of some minor differences, the overall mechanism of lipophorin rearrangements upon flight activity in the hawkmoth appears to be very similar to the known systems established for both Locusta migratoria and Manduca sexta .

Pathway of propionate synthesis in the sea mussel Mytilus edulis L.

Abstract 1. 1. An investigation was made to the presence of the enzymes participating in the propionate synthesis in mantle mitochondria of M. edulis . 2. 2. Propionyl-CoA transferase (E.C. 2.8.3.X), propionyl-CoA carboxylase (E.C. 6.4.1.3), methylmalonyl-CoA isomerase (E.C. 5.4.99.2) and methylmalonyl-CoA racemase (E.C. 5.1.99.1) are demonstrated in the mitochondrial soluble enzyme fraction. 3. 3. A scheme for the propionate synthesis in M. edulis is presented.

IN VITRO PRODUCTION OF PROPIONIC ACID IN MANTLE MITOCHONDRIA OF THE SEA MUSSEL Mytilus edulis L.

Publisher Summary This chapter focuses on parasitic organisms that usually live under hypoxic conditions, for example, the adult liver fluke Fasoiola hepatica and the intestinal roundworm Ascavis lumbricoides form volatile fatty acids mainly propionic and acetic acid for their energy supply. Propionic and acetic acid also accumulate as end products of anaerobic energy metabolism in organisms that undergo periods of hypoxia or even anoxia. It presents a study that deals with the in vitro production of propionic acid in the mantle of Mytilus edulis. It was demonstrated that the propionic acid synthesis is localized in the mitochondria. The presence of the enzymes of the pathway can be demonstrated, that is, methylmalonyl-CoA isomerase and racemase, propionyl-CoA carboxylase, and acyl-CoA transferase. The activation of the in vitro propionic acid production by malate is also observed in mantle mitochondria of Mytilus edulis . The in vivo production of propionic acid shows a lag time of approx. 16 h of anaerobiosis at 13°C before the accumulation starts. In vivo , succinate should accumulate to a certain level to induce the propionic acid production by the pathway. The production of ATP coupled to the formation of propionate is investigated.