Glánvillic acids A and B and methyl capucinoate A, new metabolites isolated from the Caribbean sponges Plakortis halichondrioides and Plakinastrella onkodes.

Glánvillic acids A (2) and B (3) and the cytotoxic cyclic peroxides methyl capucinoate A (4) and 5 were isolated from the Dominican marine sponges Plakortis halichondrioides and Plakinastrella onkodes, respectively. The structures have been elucidated by spectroscopic analysis of 4 and 5 and of methyl glánvillates A (6) and B (7).

Antimitotic diterpenes from Erythropodium caribaeorum test pharmacophore models for microtubule stabilization.

[structure: see text] Six new antimitotic diterpenes, 2-7, have been isolated from the Caribbean octocoral Erythropodium caribaeorum. Structural variations encountered in this group of natural products test recently proposed pharmacophore models for microtubule stabilizing compounds.

Enzymatic adaptations to asphyxia in the harbor seal and dog.

The activities of the glycolytic enzymes were determined in heart, liver, kidney cortex and cerebrum from the harbor seal (Phoca vitulina ) and the adult and newborn dog. Activities were similar in the four dog tissues as well as myocardium and brain tissue from both the newborn dog and seal. Most of the enzyme activities were markedly lower in kidney cortex and liver of the seal and the newborn dog, suggesting that the organs which are rendered ischemic in the diving seal or asphyxiated newborn dog have a lowered demand for glycolytic metabolism. This is perceived as an adaptation to prolong the time tissues can rely on anaerobic metabolism. Expression of the enzyme data in a 'similarity criterion' by dividing activity from an organ likely to be perfused during long diving or asphyxia (e.g., heart), by that from one rendered ischemic (e.g., kidney), yields a quotient which provides a convenient indicator of anaerobic potential. Such a treatment would reflect the contribution of a discrete tissue to the total anaerobic demand of the whole animal. The values thus generated for the glycolytic enzymes are generally higher in the seal and the newborn dog than in the adult dog, and suggest an index for determining the capacity of an animal to withstand repeated and variable asphyxia.

Regulation of enzyme activity in the hibernator. A kinetic and spectroscopic study of muscle pyruvate kinase from the Arctic ground squirrel.

Pyruvate kinase skeletal muscle of the Arctic ground squirrel was purified to homogeneity. The purified enzyme variants from the summer-active and winter hibernating squirrel appear to be identical with a near-neutral pI of 6.9 and a molecular weight of 234,000 as determined by gel filtration chromatography on Bio-Gel A-0.5m. Evidence for subunit interaction during inhibition by L-phenylalanine is demonstrated with ultraviolet derivative spectroscopy. A model for this interaction and its importance for a regulatory role are discussed. The absence of a temperature break in the Arrhenius plot for the pyruvate kinase reaction, the kinetic and physical data, and the near-neutral pI, suggest an amino acid composition that conserves the overall geometry and resultant kinetic behavior which render regulation of the enzyme insensitive to temperature.

Temperature and the regulation of enzyme activity in poikilotherms. Regulatory properties of fructose diphosphatase from muscle of the Alaskan king-crab.

1. The properties of fructose diphosphatase from skeletal muscle of the Alaskan king-crab (Paralithodes camtschatica) were examined over the physiological temperature range of the animal. 2. King-crab muscle fructose diphosphatase is first activated by Na(+) and NH(4) (+) and is then partially inhibited by these cations at concentrations higher than 10mm at 0 degrees , 8 degrees and 15 degrees C. Enzyme activity is stimulated by K(+) at 0 degrees C, but is curtailed at 8 degrees C and 15 degrees C, an effect that could render rate independent of temperature. 3. Affinity for substrate increases with decreasing temperature; below the temperature of acclimatization, K(m) for fructose 1,6-diphosphate increases, resulting in a complex U-shaped temperature-K(m) curve. 4. King-crab muscle fructose diphosphatase is inhibited by low concentrations of AMP. As with enzymes of other poikilotherms, inhibition by AMP is sensitive to temperature; the enzyme is least sensitive to inhibition by AMP near the temperature of acclimatization. 5. The affinity of fructose diphosphatase for fructose 1,6-diphosphate is enhanced by phosphoenolpyruvate, and this activation is temperature-sensitive; 0.5mm-phosphoenolpyruvate causes a sevenfold decrease in K(m) for fructose 1,6-diphosphate at 15 degrees C but a 25-fold decrease at 0 degrees C. 6. Phosphoenolpyruvate appears to decrease the affinity of king-crab muscle fructose diphosphatase for AMP at low temperature, whereas at the higher temperature it appears to enhance inhibition by AMP. Phosphoenolpyruvate was not observed to cause a reversal of inhibition of fructose diphosphatase activity by AMP. The identification of phosphoenolpyruvate as an activator of a rate-limiting step in gluconeogenesis permits the suggestion of a coupling of the controlling mechanisms of several steps in the glycolytic and gluconeogenic chains. 7. These findings suggest mechanisms for the maintenance and regulation of control of fructose diphosphatase activity in king-crab skeletal muscle at low temperature and under conditions that favour concomitant activity of phosphofructokinase.

Temperature and the regulation of enzyme activity in poikilotherms. Fructose diphosphatase from migrating salmon.

1. The calculated energy charge of the liver cell from migrating salmon is very low (0.464), in keeping with the extended starvation and high rates of muscular and biosynthetic activity of these organisms. 2. Affinity of fructose 1,6-diphosphatase for substrate increases with a decrease in temperature. 3. Arrhenius plots of the saturation kinetics are complex and suggest an interconversion of one or more forms of the enzyme; this interconversion is dependent on the identity of the cofactor. 4. Affinity of salmon fructose 1,6-diphosphatase for its allosteric inhibitor (AMP) is lower than in other fructose 1,6-diphosphatases and this enzyme-AMP interaction is largely insensitive to temperature. The functional significance of diminished AMP-sensitivity is that it allows normal or high fructose 1,6-diphosphatase activity during a low energy charge. 5. These findings suggest mechanisms for the maintenance of high rates of gluconeogenesis in salmon during spawning migration.

Temperature and the regulation of enzyme activity in poikilotherms. Properties of lungfish fructose diphosphatase.

1. The properties of fructose diphosphatase from liver of South American lungfish (Lepidosiren paradoxa) were examined. 2. Saturation curves for substrate (fructose diphosphate) and both cofactors (Mn(2+) and Mg(2+)) are sigmoidal and Hill plots of these results suggest about 2 interacting substrate and cofactor sites/molecule of enzyme. 3. Mn(2+) is an efficient positive modulator of the enzyme and K(a) for Mn(2+) is about 20-30-fold lower than the K(a) for Mg(2+). 4. Lungfish fructose diphosphatase is inhibited by low concentrations of AMP, and the affinity of the enzyme for AMP is insensitive to temperature. 5. The affinities of fructose diphosphatase for fructose diphosphate and Mn(2+) appear to be dependent on temperature, whereas affinity for Mg(2+) is temperature-independent. 6. The pH optimum of the enzyme depends on the presence of the particular cofactor. As pH increases, the K(a) values of both cations are lowered, maximum velocities are increased and the saturation curves for cofactor become hyperbolic. 7. The possible roles of these ions, pH and substrate in the modulation of fructose diphosphatase and gluconeogenic activity in the lungfish are discussed in relation to aestivation and temperature adaptation.

Temperature and the regulation of enzyme activity in poikilotherms. Properties of rainbow-trout fructose diphosphatase.

1. The properties of fructose diphosphatase from the liver of rainbow trout (Salmo gairdnerii) were examined over the physiological temperature range of the organism. 2. Saturation curves for substrate (fructose 1,6-diphosphate) and a cofactor (Mg(2+)) are sigmoidal, and Hill plots of the results suggest a minimum of two interacting fructose 1,6-diphosphate sites and two interacting Mg(2+) sites per molecule of enzyme. 3. Mn(2+)-saturation curves are hyperbolic, and the K(a) for Mn(2+), which inhibits the enzyme at high concentrations, is 50-100-fold lower than the K(a) for Mg(2+). 4. Fructose diphosphatase is inhibited by low concentrations of AMP; this inhibition appears to be decreased and reversed by increasing the concentrations of Mg(2+) and Mn(2+). Higher concentrations of AMP are required to inhibit the trout fructose diphosphatase in the presence of Mn(2+). 5. The affinities of fructose diphosphatase for fructose diphosphate and Mn(2+) appear to be temperature-independent, whereas the affinities for Mg(2+) and AMP are highly temperature-dependent. 6. The pH optimum of the enzyme depends on the concentrations of Mg(2+) and Mn(2+). In addition, pH determines the K(a) for Mg(2+); at high pH, K(a) for Mg(2+) is lowered. 7. The enzyme is inhibited by Ca(2+) and Zn(2+), and the inhibition is competitive with respect to both cations. 8. The possible roles of these ions and AMP in the modulation of fructose diphosphatase and gluconeogenic activity are discussed in relation to temperature adaptation.