Peter C. Poat

Carbohydrate metabolism in Carcinus maenas gill tissue

Abstract 1. 1. Activities of fourteen enzymes of the glycolytic, gluconeogenic and pentose phosphate pathways were measured in extracts of Carcinus maenas gill tissue. 2. 2. Lactate and α-glycerophosphate dehydrogenases had similar activities in gill extract, in contrast to mammals and insects. 3. 3. Estimation of the pyridine nucleotides showed that the total NADP(H) concentration was greater than that of NAD(H). 4. 4. Studies with 1-14C and 6-14C glucose in the presence and absence of arsenite suggest that the major portion of the C6 carbon is liberated via the citric acid cycle. 5. 5. Gill tissue was shown to have a gluconeogenic capacity. The most rapid production of glucose was observed in 50 per cent sea water when 25 per cent of the NaCl content was omitted. Under these conditions with animals collected in the winter months, November to March, and allowing for a Q 10 of two the rates observed in gill were comparable with those obtained using rat liver slices, but were much less during the summer months.

Cation transport and metabolism as a function of salinity in the excised gill of Carcinus maenas

1. 1. Intracellular concentrations of sodium and potassium were measured in the excised gill of Carcinus maenas in media of different ionic compositions as a function of salinity. 2. 2. The increase in respiration observed with decrease in salinity was independent of the activity of the conventional Na+/K+ linked pump. 3. 3. No evidence was obtained to suggest that the energy for the Na+/K+ pump was supplied by glycolysis. 4. 4. Evidence is presented which shows that the ionic composition of the medium has a pronounced effect on respiration, lactic acid and carbon dioxide production and the formation of glycogen and glucose.

Respiratoy control i mitochondria from the hepatopancreas of carcinus maenas

Abstract 1. 1. Respiratory control was demonstrated in mitochondria prepared from the hepatopancreas of the crab, Carcinus maenas. 2. 2. Addition of ADP to the mitochondria in state 4 produced only a gradual transition to state 3. This lag phase was abolished by a pre-incubation of stage 4 mitochondria with AMP. 3. 3. In the absence of phosphate, respiration was stimulated only marginally by arsenate but was not enhanced by the subsequent addition of ADP. State 3 respiration was inhibited and the P: O ratio lowered when an equimolar quantity of phosphate and arsenate was present. 4. 4. The oxidation of NAD linked substrates was inhibited 50 per cent by io μM rotenone. 5. 5. Oligomycin, DNP, and phenylethylbiguanide produced qualitatively similar effects in the crab mitochondria compared with those from mammalian sources.

An investigatin into the apparent inhibition by arginine phosphate of the activity of Carcinus maenas type-M pyruvate kinase

An enzymic synthesis utilising arginine kinase for preparing arginine phosphate in a high state of purity is described. The dissociation constant of magnesium arginine phosphate, determined by gel filtration, was 30.0 +/- 0.9 mM. That for potassium arginine phosphate was calculated to be 63.0 +/- 4.0 mM measured by the effect of potassium on the apparent magnesium dissociation constant. The effect of KCl on the reaction catalysed by the type-M pyruvate kinase from Carcinus maenas (the common shore crab) pincer and leg muscle was investigated. No effect was seen on the C. maenas pyruvate kinase activity, apart from that due to alteration of the K+ concentration, on adding up to 70 mM potassium arginine phosphate to the reaction medium. The less pure form of arginine phosphate was found to give an apparent noncompetitive inhibition of the enzyme when phosphoenolpyruvate was the varied substrate. This apparent inhibition can be accounted for by the removal of ADP from the assay medium in a side reaction involving arginine kinase and arginine phosphate. These results are discussed in terms of the possible physiological control of the type-M pyruvate kinase from C. maenas.

The regulation of pyruvate kinase in the hepatopancreas of Carcinus maenas.

Abstract 1. 1. Estimation of the activity of pyruvate kinase and pyruvate carboxylase in the hepatopancreas of Carcinus maenas gave values of 28.5 and 7.4 units/g wet wt tissue respectively. 2. 2. The concentrations of substrates, products and allosteric effectors of these enzymes in hepatopancreas were measured. 3. 3. The activities of pyruvate kinase and pyruvate carboxylase were redetermined using the approximate physiological range of substrate and effectors. 4. 4. Under these conditions the effective activity of pyruvate kinase could be decreased to less than 2 units/g wet wt tissue whereas that for the pyruvate carboxylase was 2.6 units/g wet wt tissue indicating that a net synthesis of phosphoenolpyruvate could occur in vivo .

The site of action of the diuretic ethacrynic acid on rat kidney and liver tissue

Abstract 1. 1. The action of the diuretic ethacrynic acid upon cation transport in potassium depleted/sodium loaded rat kidney cortex slices was investigated. 2. 2. No evidence was obtained to support the contention that this compound inhibits ouabain-insensitive sodium loss. 3. 3. Respiration of kidney cortex slices from both rat and guinea-pig was inhibited by ethacrynic acid. The addition of ouabain did not increase this inhibition. 4. 4. Ethacrynic acid effects cellular energy production in rat kidney and liver by a direct inhibition of mitochondrial oxidations. This is suggested as a primary site of action of the drug.

The effect of malonate on succinate metabolism in the excised gill of Carcinus maenas

Abstract 1. 1. The incorporation of radioactivity from U-14C succinate incubated with excised gill tissue of Carcinus maenas into carbon dioxide was not inhibited by malonate in 100% sea water but in 50% sea water there was a significant inhibition. 2. 2. Estimation of malonate penetration into gill tissue was complicated by the chelation of Mg2+ and Ca2+ by the inhibitor. After correcting the malonate concentration for this effect the results indicated that 49% of the intracellular water had equilibrated with the free malonate in the medium, and that decreasing the osmolarity of the latter had little effect on the permeability of the tissue to malonate. 3. 3. Evidence is presented to show that in gill tissue succinate is converted to propionate and that this conversion is stimulated by the presence of malonate in 100% sea water. 4. 4. The oxidation of 1-14C propionate was inhibited by malonate in 50% sea water, but it was almost invariably without effect or stimulated propionate oxidation in 100% sea water. 5. 5. Incorporation of radioactivity into lipids from succinate or propionate was also found to be stimulated by malonate in 100% sea water. The majority of the radioactivity in the lipid fraction was located in glycerol.