Albertus de Zwaan

4 – Carbohydrate Catabolism in Bivalves

Publisher Summary This chapter focuses on the variety and flexibility of pathways of carbohydrate catabolism in bivalves. In the presence of oxygen, glucosyl units are completely oxidized to H2O and CO2. Dehydrogenation occurs in glycolysis and the citric acid cycle; via the coenzymes NAD or FAD and the electron-transfer chain, the hydrogen is oxidized to H2O by atmospheric oxygen; CO2 is formed in the citric acid cycle, and both end products are formed in the mitochondrion. In nerve tissues and to a lesser extent in organs such as the heart, in the absence of oxygen, the same cooperation still exists among glycolysis, the citric acid cycle, and the electron-transfer chain, but that oxygen is replaced by a prestored electron acceptor—the yellow lipochrome pigment. The pigment is composed of neutral fats and phospholipids, and unsaturated fatty acids serve as the endogenous electron-acceptor molecules. The organelles rich in the yellow pigment are called cytosomes. Cytosomes accumulate bivalent cations in the absence of oxygen.

Anaerobic glucose degradation in the sea mussel Mytilus edulis l.

Abstract 1. 1. The distribution of radioactivity over different classes of chemical compounds from glucose- ul - 14 C injected into the sea mussel Mytilus edulis was examined after 24 and 48 hr of anaerobiosis. 2. 2. The amino- and organic acids together incorporated about 85 per cent of the total radioactivity of mussel homogenate both after 24 and 48 hr of anaerobiosis. 3. 3. The incorporation of radioactivity by the amino acids was mainly confined to alanine and glutamic acid. The level of alanine remained much the same after 24 or 48 hr of incubation but the level of glumatic acid increased. 4. 4. The incorporation of radioactivity by the organic acids was mainly confined to succinate.

5 – Carbohydrate Metabolism of Gastropods

Publisher Summary This chapter discusses the carbohydrate metabolism of gastropods. D-glucose is the most common monosaccharide and has been detected in the blood and tissues of many gastropods. Other sugars also occur, in particular D-galactose, that are either stereoisomers or derivatives of monosaccharides. Glycogen and galactogen are the main storage polysaccharides. Whereas glycogen occurs in most gastropod tissues and serves as a general energy source, galactogen is generally confined to the albumen gland and eggs of adult pulmonate snails and the albumen gland region of the palliai oviduct of some prosobranchs, and it serves as a specialized energy source in reproduction. Glycogen is a branched-chain homopolysaccharide of D-glucose in α-1,4 linkage with branches joined through α-1,6 linkages. The degree of branching and the length of the outer branches of the glycogen from the snail Biomphalaria glabrata are similar to those of glycogens from other animal sources.

Control of glycolysis in the posterior adductor muscle of the sea musselMytilus edulis

SummaryConcentrations of glycolytic intermediates, lactate, adenine nucleotides, inorganic phosphate, phosphoarginine and citrate have been estimated after various periods of valve closure (Table 1 and Fig. 1). Mass action ratios of enzyme steps involved in the metabolism of these components are compared with their equilibrium constants. This reveals glycogen phosphorylase, phosphofructokinase, hexosediphosphatase and pyruvate kinase catalyze non-equilibrium reactions. The first three enzymes possess relatively low activities (Table 2).From the changes in concentrations of the glycolytic intermediates it is concluded that phosphofructokinase controls the carbon flow during the first hours after valve closure, whereas later on the rate of conversion of phosphoenolpyruvate is determining this flow. In skeletal muscle phosphofructokinase controls the carbon flow during the whole period of exercise.The concentrations of ADP, AMP and inorganic phosphate increase, whereas the concentrations of ATP, phosphoarginine and citrate decrease during valve closure (Table 1 and Fig. 2). In contrast to skeletal muscle, these changes do not result in a strong increase in the glycolytic flux.There is a much greater potential for ATP hydrolysis by the myofibrillar ATPase system than is actually realized by the adductor muscle during valve closure.

Glycogen degradation and end products of anaerobic metabolism in the fresh water bivalveAnodonta cygnea

Summary1.Glycogen levels and the production of metabolic end products by the fresh water bivalveAnodonta cygena were determined under aerobic and anaerobic conditions.2.The glycogen content accounts for 5–14% of the dry weight. After 30 hours of aerobic or anaerobic incubation no significant glycogen breakdown could be observed.3.L-lactate and alanine seem to be only initial end products, whereas succinate increases continuously during the first 15 hours.4.Anodonta cygnea also accumulates volatile fatty acids during anaerobiosis. After 30 hours of anoxia 30.1 and 46.0 μmol g−1 dry weight of acetate and propionate respectively are formed. In fact the volatile fatty acids account together for about 75% of the total accumulated end products.

Studies on the phylogenetic distribution of pyruvate oxidoreductases

Abstract Lactate dehydrogenase is present in all phyla examined. Alanopine and strombine dehydrogenase activities are present in all major phyla except the Arthropoda, Echinodermata and Chordata. Octopine dehydrogenase is also absent from the latter phyla and virtually absent from the Annelida. The opine dehydrogenase activities are generally absent from non-marine species. Relationships can be observed between malate dehydrogenase and glutamic-oxaloacetic transaminase and between the latter and glutamic-pyruvic transaminase in certain phyla. The results support the suggestion that the opine pathways are used in tissues to generate high (relatively) rates of energy production.

The effect of phosphoenolpyruvate, fructose 1,6-diphosphate and pH on allosteric pyruvate kinase in muscle tissue of the bivalve Mytilus edulis L

1. 1.|Pyruvate kinase (ATP:pyruvate phosphotransferase, EC 2.7.1.40) in muscle tissue of the sea mussel Mytilus edulis possesses properties which are similar to allosteric L-type pyruvate kinase of the rat liver with respect to stimulation by phosphoenolpyruvate and Fru-1,6-P2. The action of these modulators is pH dependent. In contrast to L-type there is an increasing stimulation by phosphoenolpyruvate and Fru-1,6-P2 by lowering the pH within the range from 8 to 6. 2. 2.|A possible regulatory role of the pH influence on enzyme activity is discussed.

Anaerobic energy metabolism of the scavenging isopodCirolana borealis (Lilljeborg)

Summary1.Cirolana borealis utilises glycogen during anaerobiosis and shows a marked Pasteur effect. In 18h, 20–30 mg/g dry weight were converted, about half of the initial total glycogen content (Table 1).2.Lactate is the major end product, while succinate and alanine are minor end products. 27–52% of the lactate produced was excreted into the incubation water (Tables 2 and 3). A good stoichiometric relationship was obtained between the glycogen consumed and the accumulation of these end products.3.Small amounts of glutamate and aspartate contribute to the carbon flow, which could be of significance for obtaining redox balance (Table 3).4.ATP production during anoxia was 75% of that during the standard aerobic state.5.It is concluded that anaerobic fermentative metabolism ofC. borealis is adapted to maintain a high ATP output per unit time, which suits the high energy demand under natural anaerobic conditions.6.WhenC. borealis are subjected to experimental anoxia they expel their gut contents and the incubation water becomes enriched with acetate, propionate, and amino acids. Most of these compounds probably stem directly from the gut content, while some, like acetate, may be produced by microbial activity. Starvation and anaerobic preincubation resulted in a marked lowering of the amounts of these compounds in the incubation water.

Phosphoenolpyruvate carboxykinase from adductor muscle tissue of the sea musselMytilus edulis L.

Summary1.PEP-carboxykinase from sea mussel adductor muscle exhibits activity with Mn++, Mg++ and Zn++.2.Ca++ inhibits the enzyme in the presence of Mg++ or Zn++, but has almost no effect on activity with Mn++.3.The pH activity profiles depend on the cation used; the optima are reached at pH 6.6, 6.7 and 6.0 for Mn++, Mg++ and Zn++ respectively.4.Lineweaver-Burk plots for PEP1 are linear. Between pH 6.0 and 7.3 with Zn++ theKm(PEP) is independent of the pH and has a value of 0.20 mM; with Mn++ or Mg++ theKm(PEP) values decrease by increasing the pH value from 6.6 to 7.3 (Mn++, 2.66→0.23mM; Mg++, 1.48→0.46 mM).5.In the presence of Mn++, Mg++ and Zn++, ITP shows competitive inhibition with respect to PEP.6.Alanine, succinate and fructose-1,6-diphosphate have no influence on catalysis by PEP-carboxykinase.7.Pyruvate kinase and PEP-carboxykinase activities are detected in adductor muscle, hepatopancreas, gill and mantle. Both enzymes show by far the highest activity in adductor muscle.8.At pH 7.3 pyruvate kinase activities are much higher when compared with PEP-carboxykinase, but at pH 6.5 and low PEP concentration, PEP-carboxykinase activities are higher.

Pyruvate kinase in muscle extracts of the sea mussel Mytilus edulis L.

Abstract 1. 1. Pyruvate kinase activity in fresh extracts from the posterior adductor muscle of the sea mussel, Mytilus edulis, shows allosteric properties in contrast to skeletal pyruvate kinases of mammals. 2. 2. The Hill plot at [PEP] ∗ = ∞ shows positive co-operativity (nH = 1·3) with respect to PEP. 3. 3. The sigmoidicity of the substrate concentration-velocity curve is strongly increased in the presence of alanine (inhibition). The Hill coefficient increases from 1·3 to 1·8 whereas the Km app. for PEP changes from 0·65 to 1·58 mM. 4. 4. Pyruvate kinase activity is also strongly inhibited by ATP. 5. 5. Inhibition of pyruvate kinase activity by alanine and ATP is counteracted by FDP. 6. 6. The properties of pyruvate kinase might explain why a part of PEP is available for succinate production during anaerobic glycolysis.