Adipokinetic hormones concentrations in the haemolymph of Schistocerca gregaria, measured by radioimmunoassay.

A new procedure for the measurement of adipokinetic hormone (AKH) concentrations in locust (Schistocerca gregaria) haemolymph is described: Haemolymph is extracted with chloroform/methanol/water and the aqueous layer is fractionated with reverse-phase cartridges and HPLC. The fractions corresponding to AKH-I (Lom-AKH-I) and AKH-II (Scg-AKH-II) are then measured in a competitive binding assay using specific antibodies and [3H]AKHs. The procedures could be applied to any peptides containing N-terminal pyroglutamate residues including all members of the adipokinetic/hyperglycaemic/red pigment concentrating hormone family. Results show that the concentrations of both AKH-I and AKH-II increase within 5 min of initiation of flight and are maintained at approx. 15-fold (AKH-I) and 6-fold (AKH-II) the resting levels over flights of at least 60 min. Poisoning of locusts with either the insecticide deltamethrin or with potassium chloride also caused release of hormones. Starvation for 6 h caused elevation of hormone levels in 5th instar nymphs, but starvation for 6 or 20 h had little effect on hormones in adults, despite an increase in haemolymph diacylglycerols at 20 h.

Influences of pH on human platelet metabolism.

The intracellular pH of human platelets is affected by external pH and by the addition of metabolic substrates and analogues. Acetate and propionate decrease pH in a rapid concentration-dependent manner, whereas glucose decreases the internal pH at a slower rate which is independent of concentration above 0.3 mM. The mechanisms of these effects is discussed. The rate of metabolism of glucose to lactate in human platelets was strongly pH-dependent, with higher rates at more alkaline pH values. This effect was found for several different buffer systems. Addition of acetate caused an inhibition of glycolysis, whereas addition of propionate had little effect. The rate of the oxidative pentose phosphate pathway also increased with increasing pH and this pathway was inhibited by both acetate and propionate. It is proposed that the effect of acetate on glycolysis required the metabolism of the acetate, whereas the effect of both acetate and propionate on the pentose phosphate pathway are directly due to the decrease in internal pH. The oxidation of acetate to carbon dioxide showed only small pH-dependent changes in rate unless glucose was also present: glucose inhibited oxidative metabolism (the 'Crabtree Effect'), but this inhibition was only apparent at higher pH values when glycolytic rates were high.

Citrate metabolism by human platelets.

As part of a study on the utilization of substrates by platelets in defined media the metabolism of citrate was measured, since citrate is a common anticoagulant of nearly all such media, and is also an intermediate of oxidative metabolism. Human platelets transferred from plasma to an artificial medium by gel filtration, were incubated with [14C]citrate at 22 degrees C and labelled carbon dioxide produced was measured during short-term incubations of 2 h. Citrate (1 mM) was oxidized to carbon dioxide at low (0.3 nmol per 10(9) platelets h-1) but significant rates, and the oxidation was decreased by the presence of an alternative substrate (acetate) in the medium. There was, however, no significant conversion of citrate to glycogen. It was calculated that under normal storage conditions of platelet concentrates for transfusion purposes, the amount of citrate used cannot decrease citrate concentrations sufficiently to bring about platelet activation.

Separation of insecticidal components from an extract of the roots of male Piper guineense (west African black pepper) by gas chromatography.

A petroleum ether extract of Piper guineense male roots showed insecticidal activity when tested against Musca domestica. Gas chromatography of the extract yielded four active fractions, one of which was a pure component which was identified by spectral and chemical methods as pellitorine (N-isobutyl-2E,4E-decadienamide). The root extract lost about half of its insecticidal potency during passage down the GLC column, and much of the residual activity was due to the presence of pellitorine. It was concluded that GLC facilitates the isolation of active components in a pure form, but causes some insecticidal components of the root extract to be lost.

The biochemical composition of venom from the pavement ant (Tetramorium caespitum L.).

The venom of the pavement ant, Tetramorium caespitum, is used for prey capture, defense and social communication. The venom is predominantly proteinaceous in nature and contains various free amino acids, predominantly aspartic and glutamic acid, as well as histamine. The activities of the enzymes phospholipase and hyaluronidase, which are believed to be present in all hymenopteran venoms could not be detected. The composition of Tetramorium caespitum venom is compared with other myrmicine venoms.

The regulation of glycolysis in perfused locust flight muscle.

Concentrations of glycolytic intermediates, amino acids and possible regulator substances were measured in extracts from locust thoracic muscles perfused under different conditions. The conversion of [(14)C]glucose into intermediates and CO(2) by muscle preparations was also followed. When muscles perfused with glucose were made anaerobic changes in metabolite concentrations occurred that could be accounted for by an activation of phosphofructokinase and pyruvate kinase. When butyrate and glucose were present in the perfusion medium the rate of glycolytic flux was lower than with glucose alone, and the aldolase reaction appeared to be inhibited. When butyrate alone was supplied to the muscle the concentrations of most glycolytic intermediates were similar to those found when glucose was supplied. Iodoacetate caused changes in concentrations of intermediates that appeared to result from inhibition of glyceraldehyde 3-phosphate dehydrogenase. Fluoroacetate-poisoned muscles showed a high citrate concentration, but no obvious site of inhibition by citrate was apparent in the glycolytic pathway. Mechanisms for control of glycolysis in locust flight muscle are discussed and related to the known properties of isolated enzymes. It is proposed that trehalase, hexokinase, phosphofructokinase, aldolase, and pyruvate kinase may be control enzymes in this tissue.

Occurrence and metabolism of scylloinositol in the locust.

1. scylloInositol has been identified as a component of locust haemolymph, where it occurs in concentrations of 0.2-0.4mg./ml. 2. A simple method for the identification of scylloinositol is described. This has been used to demonstrate the presence of scylloinositol in five other insect species. 3. Locust phospholipids contain myoinositol but no scylloinositol. 4. Radioactivity from [(14)C]glucose is incorporated into myoinositol and scylloinositol by the locust in vivo. 5. Extracts of locust fat body catalyse the conversion of myoinositol into scylloinositol. This seems to take place by a two-step process in which myoinositol is first oxidized with NAD(+) to myoinosose-2, and the myoinosose-2 is stereospecifically reduced with NADPH to scylloinositol.

3-O-methyl-D-mannose from Streptomyces griseus.

1. Streptomyces griseus was grown in a medium containing l-[Me-(14)C]methionine, and the labelled products from an ethanolic extract of the cells were examined. 2. Acid hydrolysis of one of the products gave a compound identified as 3-O-[Me-(14)C]-methylmannose by a series of degradative reactions. 3. Reduction of the radioactive compound gave 3-O-methyl-d-mannitol, indistinguishable from a synthetic sample.