Theoretical analysis of the effects of two pH regulation patterns on the temperature sensitivities of biological systems in nonhomeothermic animals

pH-temperature interactions on protein function and hibernation: GDP binding to brown adipose tissue mitochondria

1. [3H]GDP binding to the uncoupling protein of brown adipose tissue was determined on mitochondria isolated from hibernating European hamsters, at two temperatures, 35 and 15 degrees C, and four values of 25pH (pH corrected to 25 degrees C): 6.4, 6.8, 7.2 and 7.6, encompassing the physiological range of pH. Buffer composition was adjusted to get the same pH-temperature relationship as for mammalian blood, in which this relationship is mainly determined by protein imidazole buffers. 2. The maximal binding capacity was independent both of temperature and pH. The dissociation constant KD was highly pH-dependent, but was independent of temperature when 25pH was held constant. Under these conditions, the uncoupling protein thus fully conserves its regulatory properties over the temperature range studied (eurythermal adaptation). 3. The temperature coefficient of the apparent pK' for the pH effect (-0.012 +/- 0.004) differed significantly from that of GDP terminal phosphoryl group, but not from that of blood protein imidazole buffer groups, in good agreement with the imidazole alphastat theory. 4. The results indicate that GDP reaction with the protein involves an electrostatic binding with a titratable group of the protein, probably a sulfhydryl. 5. pH modulation of the uncoupling of brown adipose tissue mitochondria probably permits a reversible control of thermogenesis in the hibernation cycle, heat dissipation being inhibited by respiratory acidosis in deep hibernation, but facilitated by the hyperventilation of arousal.

Distribution and properties of lactate dehydrogenase isoenzymes in red and white muscle of freshwater fish

The distribution and kinetics of LDH isoenzymes in red and white muscles of 5 species of salmonids, 4 species of cyprinids and one coregonid species were studied. In all species the white muscles are characterized by the occurrence of only the most cathodic isoenzymes, or groups of isoenzymes. The red muscles contained either the full set of isoenzymes (cyprinids) or a selection in which the anodic forms dominated (salmonids, coregonid). The most striking difference between the two types of muscle was met inCoregonus sp. The temperature profiles of pyruvate affinity are similar in all species of fish studied. On the other hand, Km(pyr) values and degree of pyruvate inhibition are closely related and vary greatly with temperature, with the taxonomic position (and thus biology) of the species, and with electrophoresic mobility of the isoenzyme. Highest affinity and strongest inhibition occurred in the anodic (H4) isoenzymes of cyprinids at low temperature; lowest affinity and zero inhibition in the cathodic isoenzymes (Mα4 → Mβ4) of salmonids and coregonids at high temperature. In salmonids the more recently duplicated loci of the M-group of isoenzymes possess identical Km values at all temperatures, whereas the two older M and H loci differ greatly in this respect. Thus the more recent duplication of LDH loci in salmonids and coregonids may be seen as a mechanism by which the tetramers required for LDH activity can be constructed from more closely related subunits than are provided by the older M and H loci.Some problems in connection with the determination of the kinetic constants of the lactate oxidase reaction are discussed and it is suggested that an alkaline, pyruvate trapping system provides conditions which are more realistic than those of other assay systems. The Km(lactate) values found are in the biological range and, at 20°C, provide further circumstantial evidence that the red muscles of fish should be capable of oxidizing the lactate produced by the white muscles during strenuous exercise. At 4°C the Km(lactate) values are abnormally high in all muscle preparations and thus are not correlated with the Km(pyruvate) values which are lowest at this temperature.

Effect of temperature on intracellular pH in crayfish neurons and muscle fibers

Intracellular pH microelectrodes were used to determine the effects of temperature (13-26 degrees C) on the in vitro regulation of intracellular acid-base status of neurons and muscle fibers of the crayfish Astacus leptodactylus. The values of the temperature coefficients delta pH/delta T (pH unit/degrees C) were -0.019 and -0.026 for muscles and neurons, respectively, values which are close to the temperature coefficient (-0.019) of the pK' of protein imidazole buffer groups. When temperature varies, the dissociation ratio of imidazole groups is thus maintained by the cellular regulation of cytoplasmic pH. According to the alphastat regulation hypothesis, this constancy would minimize the temperature effects on enzymic systems.

Temperature dependence of intracellular pH in higher plant cells : A (31)P nuclear magnetic resonance study on maize root tips

The recent introduction of (31)P nuclear magnetic resonance spectroscopy offers a new approach to the problem of obtaining a simultaneous and direct evaluation of both the cytoplasmic and vacuolar pH in higher plant cells (J. K. M. Roberts, P.M. Ray, N. Waderlardetzky and O. Sardetzky, 1980, Nature 283, 870-872; 1981, Planta 152, 74-78). Using this method we have been able to detect a selective pH decrease of about 0.5 units at the level of the cytoplasmic compartment of maize root tips when the temperature was increased from 4 to 28°C. This effect was completely reversible with temperature. No pH variation could be detected at the level of the vacuolar compartment.

Malate dehydrogenase isozymes in the longnose dace, Rhinichthys cataractae

The interspecies homology of dace supernatant (A2,AB,B2) and mitochondrial (C2) malate dehydrogenase isozymes has been established through cell fractionation and tissue distribution studies. Isolated supernatant malate dehydrogenase (s-MDH) isozymes show significant differences in Michaelis constants for oxaloacetate and in pH optima. Shifts in s-MDH isozyme pH optima with temperature may result in immediate compensation for increase in ectotherm body pH with decrease in temperature, but duplicate s-MDH isozymes are probably maintained through selection for tissue specific regulation of metabolism.