Many groups of invertebrates use metabolic strategies that do not lead to the accumulation of lactate during periods of hypoxia or anoxia. These animals may accumulate some combination of the following: alanine, octopine, alanopine, strombine, acetate, propionate, 2-methylbutyrate, 2-methylvalerate, and succinate. An organism may derive a benefit from production of an alternative end product when the yield of ATP per mole of glucose 6-phosphate is greater than that found in lactate production. Formations of succinate, propionate, 2-methylbutyrate, and 2-methylvalerate have been shown to yield more ATP in a few species. This analysis can be extended to the formation of alanine, as this is accompanied by the conversion of aspartate to succinate .Formations of octopine, alanopine, or strombine apparently do not increase the yield of ATP per mole of glucose 6-phosphate, because the enzymes forming these compounds are functionally analogous to lactate dehydrogenase. A potential advantage of producing these compounds might be maintenance of a constant intracellular osmotic pressure during periods of anoxia. The significance of this is uncertain, because if lactate were to accumulate, the expected change in osmotic pressure appears to be trivial. Another possible advantage of accumulating octopine, alanopine, or strombine, would be the ability to maintain a lower NADHNAD+ ratio as compared with the accumulation of lactate. This might assist the organism in maintaining a high rate of glycolysis by reducing the inhibition of glyceraldehyde 3-phosphate dehydrogenase by NADH. Other possibilities are smaller perturbations of the acid-base balance of the cell, or producing a compound that has less effect on the catalytic and regulatory properties of enzymes in the cell.Most organisms on this planet are dependent on oxygen for their survival, yet many live in habitats that subject them to periods of hypoxia or anoxia. Bacteria are the champions at adapting to hostile habitats, but that topic is beyond the scope of this article, which is restricted to an examination of a few invertebrates. Some of these use anaerobic metabolism to fuel short bursts of intense muscular activity, when aerobic processes cannot meet the metabolic demand. Others, such as those found in the intertidal region, are subjected to variable periods of hypoxia, while many that are endoparasitic can survive indefinitely without oxygen, perhaps not even using aerobic processes to generate ATP in the presence of oxygen (von Brand, '66; Saz, '81) ANAEROBIC END PRODUCTS This process has been exploited by commercial and amateur interests throughout most of man's recorded history. The other anaerobic process of historical note is the production of lactate associated with muscular activity in vertebrates. This process has received considerable attention from biologists; hence, the conversion of glycogen to lactate has become the most familiar anaerobic pathway. Lactate production, however, is not a universal feature of anaerobic metabolism in the animal ...

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1978. Alterations in energy metabolism associated with the transition from water to air breathing in fish. Can. J. Zool. 56: 730-735. Hoplios malaharicus and Hoplerythrin~rs rrniturniatrrs are two closely related species which live in poorly oxygenated water. The former is an obligate water breather, whereas the latter has the additional capacity to respire atmospheric oxygen through a highly vascularized swim bladder. Hoplcrythrin~rs has greater lipid stores than Hoplitrs and probably places a greater dependence upon this metabolic fuel as an energy source than Hoplios. In contrast with this, Hoplirrs has greater heart and liver glycogen reserves than Hopleryrhrinrrs. Hoplias hearts perfused in vitro with buffer containing cyanide continued to beat eight times longer than Hoplepthrir~rrs hearts. The performance of both types of hearts was markedly increased when glucose was added to the perfusate; however, the Hoplias hearts still continued to function better than the Hoplrrythrinus hearts. It is concluded that the Hoplias heart is better adapted to function anaerobically than the Hoplerythrinlts heart. DRIEDZIC, W. R., C. F. PHLEGER, J. H. A. FIELDS et C. FRENCH. 1978. Alterations in energy metabolism associated with the transition from water to air breathing in fish. Can. J. Zool. 56: 730-735. Hoplias malabaricus et Hoplerythrinus unitaeniatus sont deux especes parentes vivant dans un milieu aquatique peu oxygene. Hoplerythrinus est un poisson a respiration aquatique obliga-toire, alors qu'Hoplias possede la propriete additionnelle de pouvoir respirer I'oxygene atmospherique par le tmchement d'une vessie natatoire tres vascularisee. Hoplerythrinus met plus de lipides en reserve qu'Hoplias et depend probablement plus aussi de ce produit de metabolisme comme source d'energie. Chez Hoplias, en revanche, le coeur est plus gros et les reserves de glycogene hepatique plus importantes. Des coeurs d'Hoplias en perfusion in vitro dans une solution-tampon contenant du cyanure continuent de battre huit fois plus longtemps que les caeurs d'Hoplerythrinus. Du glucose ajoute au perfusat ameliore la performance des deux types de cceurs, mais les coeurs d'Hoplias continuent de fonctionner mieux que ceux d'Hoplerythrinus. Le coeur d'Hoplias semble donc mieux adapt6 a une vie anaerobique que le caeur d3Hoplerythrinus.[Traduit par le journal] Introduction sphere through a highly vascularized swim bladder Hoplias ,nn/nharicus and Huplerythr.inus uni-(Carter and Beadle 193 1). Laboratory studies have tcrerziatus are two closely related fish in the family shown that Hoplerythrinus extracts about 25% of Erythrinidae which differ in one important charac-l t~ oxygen requirement through the swimbladder teristic. Hoplias is an obligate water breather when held in normoxic water, but as the oxygen (Johansen 1970), whereas Hoplerythrinus has the content of the water decreases a greater ~r o~o r t i o n capability of extracting oxygen from the atmo-of the required oxygen is derived from the atmosphere (

The terminal step in the anaerobic glycolysis of muscle in the chambered nautilus, Nautilus pompilius, is not pyruvate reduction to lactate as in vertebrate muscle. Instead of lactate dehydrogenase, these organisms utilize octopine dehydrogenase (E.C. 1.5.1.11), catalyzing the reductive condensation of pyruvate and arginine, which is dependent on the reduced form of nicotinamide adenine dinucleotide, to form octopine and the oxidized form of the coenzyme. The kinetic properties of octopine dehydrogenase favor the production of octopine, which accumulates under a variety of conditions.

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Octopine dehydrogenases from the mantle muscle of the squid, Symplectoteuthis oualaniensis, and of the octopus, Octopus ornatus, were kinetically characterized and compared. In the squid, the specific activity of the enzyme was about 110 μmol product formed per minute per gram wet weight; in the octopus that value was over 600. Both enzymes show similar pH dependence; in the direction of octopine formation the pH optimum was about 6.5, whereas in the direction of octopine oxidation it was about 8.5. The affinities for NADH, arginine, and pyruvate were similar (Km values were about 0.04 mM, 7 mM, and 2 mM respectively). Increasing the concentration of either arginine or pyruvate increased the affinity for the cosubstrate (pyruvate or arginine), this mechanism being a means of regulating the enzyme activity in vivo. In the direction of octopine oxidation, the octopus enzyme showed a much higher affinity for octopine (Km = 0.8 mM) than did the squid enzyme (Km = 4.4 mM), suggesting that it may be better geared for reconverting octopine to arginine and pyruvate after anaerobic bursts of muscle activity.

Alanopine dehydrogenase (alanopine : NAD oxidoreductase) was purified from the adductor muscle of the Japanese oyster, Crassostrea gigas Thunberg. This enzyme catalyzes the reductive imination between pyruvate and alanine, or glycine, utilizing NADH as coenzyme, producing 2,2'-iminodipropionic acid (alanopine), or 2-methyliminodiacetic acid (strombine). The enzyme can be readily purified to a specific activity of 700 units/mg protein. The molecular weight was 47000 f 4000 when measured by gel filtration on Sephadex G-200, or by electrophoresis on 10% polyacrylamide gels in the presence of 1 "/, sodium dodecyl sulphate. The latter value was unaltered by treatment with 8 M guanidine hydrochloride, suggesting that alanopine dehydrogenase is composed of a single polypeptide. Of the keto acids tested for activity with the enzyme, only pyruvate and 2-oxobutyrate reacted significantly as substrates; among the amino acids tested, highest activities occurred with alanine and glycine, but 2-aminobutyrate and serine also reacted as substrates. Apparent K,,, values obtained for the substrates are 0.01 mM, 0.45 mM, and 100 mM for NADH, pyruvate and alanine (or glycine) respectively when measured at approximately saturating concentrations of cosubstrates at pH 7.0. The product, NAD' was found to be a competitive inhibitor with respect to NADH, and the low apparent K i for NAD+ (0.22 mM) at pH 7.0 may indicate that the enzyme is closely regulated by the redox status of the cell. Several metabolites were tested for possible effects on the enzyme; of these ATP, ADP, AMP, succinate and 2-oxoglutarate were inhibitors. The adenylates inhibited competitively with NADH. The inhibition by 2-oxoglutarate was uncompetitive with respect to alanine and pyruvate, in both cases the apparent Ki value being 0.7 mM at pH 7.0. Succinate inhibition was non-competitive with respect to alanine and pyruvate, the apparent K i values being strongly dependent on pH (22.0 mM, 6.5 mM, and 1.8 mM at pH 7.5, 7.0, and 6.5 respectively). The physiological role of the enzyme during anaerobiosis is discussed.Bivalve molluscs living in the intertidal region have developed mechanisms to cope with exposure stress, enabling them to survive during low tide. One predominant mechanism is valve closure, which results in hypoxic or anoxic conditions in the mantle fluids [l] phosphopyruvate carboxylase and pyruvate kinase. Studies on the kinetic and regulatory properties of these enzymes in M . edulis and Crassostrea gigas [12-161 resulted in a hypothesis for the regulation of these enzymes by intracellular pH, alanine, and fructose 1,6-bisphosphate such that phosphopyruvate carboxylase would be activated under anaerobic conditions while the activity of pyruvate kinase would be reduced . The other area of interest has been the source of amino nitrogen required for the synthesis of alanine, where two conflicting hypotheses have been proposed. The first proposal suggested that alanine formation is coordinated with aspartate depletion through a couple between alanine amin...