The regulation of the intracellular pH in cells from vertebrates

Eukaryotic cells control their intracellular pH using ion-transporting systems that are situated in the plasma membrane. This paper describes the different mechanisms that are involved and how their activity is regulated.     

Subunit size of enzymes and genetic heterozygosity in vertebrates

There is a small but significant positive correlation between individual locus estimates of heterozygosity and subunit molecular weight in vertebrate dimeric enzymes. This correlation is smaller than that previously shown to exist for Drosophila dimers, and some possible reasons for this are explored. Data for vertebrate tetrameric enzymes are less extensive but appear to give similar trends to those shown by dimers. It is concluded that enzyme heterozygosity is influenced by both subunit size and quaternary structure.     

Activities of adenylate-degrading enzymes in muscles from vertebrates and invertebrates

Activities of adenylate-degrading enzymes in muscles of vertebrates and invertebrates were determined. Mammalian and fish muscles showed a markedly higher activity of AMP deaminase with a lower level of adenosine deaminase and 5'-nucleotidase. Cephalopods showed an active adenosine deaminase and a 5'-nucleotidase which preferred AMP as the substrate. Negligible deamination of AMP and adenosine and little phosphohydrolase activity toward AMP and IMP were observed in the shellfish muscles. Adenine nucleotides can be degraded to form IMP via the AMP deaminase reaction in vertebrate muscles, while dephosphorylation of AMP to adenosine, which is then converted to inosine, appears to proceed in cephalopods. Adenylates can be hardly degraded in shellfish muscles.     

Comparison of liver mixed-function oxygenase and antioxidant enzymes in vertebrates

We performed a comparative analysis of cytochrome P450, cytochrome b5, MFO associated enzymes and cytosolic antioxidant enzymes in hepatic microsomes and cytosolic fractions prepared from five animal species representing three vertebrate classes living in tropical conditions (Brazil). The data obtained show that rats have higher hepato-somatic index, specific cytochrome b5 concentration, and NADPH-dependent cytochrome c (P450) activity compared to ectothermic species, SOD activity similar to those in amphibians, and specific concentration of cytochrome P450 and catalase activity lower than in a toad, but higher than in fishes and a frog. Our data indicate that tropical fishes may have reduced xenobiotic-metabolizing ability compared to the rat and amphibians. In contrast to fish and rat, amphibians have a low ratio (< 0.5) of cytochrome b5 concentration to that of P450. Most species showed cytochrome b5 sensitivity to oxygen. Thus, the use of sodium dithionate as a reducer, rather than NADPH, may be preferential in b5 determinations.     

Odorant and pheromone receptor gene regulation in vertebrates

The largest mammalian gene family codes for odorant receptors and is exclusively devoted to the perception of the outside world. Its expression is very peculiar, since olfactory sensory neurons are only allowed to express a single of its numerous members, from a single parental allele. How this is achieved is unknown, but recent work points to multiple regulatory mechanisms, possibly shared by pheromone receptor genes, acting at (a) a general level, via the expression of the chemoreceptor itself and (b) a more restricted level, defined by activator elements.     

The regulation of ammonia assimilating enzymes in Lemma minor

Summary Lemna minor has the potential to assimilate ammonia via either the glutamine or glutamate pathways. A 3-4 fold variation in the level of ferredoxindependent glutamate synthase may occur, when plants are grown on different nitrogen sources, but these changes show no simple relationship to changes in the endogenous pool of glutamate. High activities of glutamate synthase and glutamine synthetase at low ammonia availability suggests that these two enzymes function in the assimilation of low ammonia concentrations. Increasing ammonia availability leads to a reduction in level of glutamate synthase and glutamine synthetase and an increase in the level of glutamate dehydrogenase. Glutamine synthetase and glutamate dehydrogenase are subject to concurrent regulation, with glutamine rather than ammonia, exerting negative control on glutamine synthetase and positive control on glutamate dehydrogenase. The changes in the ratio of these two enzymes in response to the internal pool of glutamine could regulate the direction of the flow of ammonia into amino acids via the two alternative routes of assimilation.Abbreviations GS Glutamine synthetase - GDH Glutamate dehydrogenase - GOGAT Glutamate synthase     

Organic osmolyte channels in cell volume regulation in vertebrates

Volume-activated organic osmolyte channels are found in a variety of vertebrates and cell types and show both common and disparate features. Upon exposure to hypotonic conditions, organic compounds such as taurine are released through these channels, reducing the intracellular solute concentration and thereby restoring cell volume. Various structurally diverse membrane proteins have been proposed as the channel. Accumulating evidence suggests that some of these proteins may play a more significant role as regulators than as the channel itself. Intracellular ionic strength may also modulate the release of organic osmolytes through these channels.     

Variation of loci encoding homologous enzymes in an evolutionary series of vertebrates

A study of variability of 11 allozyme loci (sAat, G3pdh, Gpi, sIdh, Ldh-A, Ldh-B, sMdh, sMe, sSod, Pgdh, and Sdh) in the evolutionary series of vertebrates from Cyclostomat to Mammalia revealed that (1) in vertebrates, these loci encoding multimeric enzymes are characterized by different heterozygosity levels, the extremes of which (represented by loci Ldh-A and Pgdh) differ from each other more than by a factor of 4; (2) classes of vertebrates markedly differed from one another in genetic variation; lower Tetrapoda are characterized by the highest level of genetic polymorphism, the classes representing the margins of the phyletic line-primitive (Cyclostomata and Chondrchthyes) and advanced (Aves and Mammalia)--have minimum heterozygosity levels, whereas Osteichthyes are characterized by intermediate heterozygosity level; (3) in the evolutionary series of vertebrates, heterozygosity varies rather independently in the groups of loci characterized by low, medium, and high variability. These patterns are explained in the context of intraorganismic factors: integration of mono- and polygenic traits (primarily, body size and ontogeny rate) and evolutionary specialization.     

Neurotrophic regulation of the restorative processes in muscle autografts in vertebrates

In frogs, tortoises and rats autotransplantation of the whole gastrocnemius muscle has been performed into its own bed at sewing the nerve to the autotransplant and at its denervation. Fragments of the skeletal muscles are also transplanted into the brain and into the spinal cord in frogs and rats. By means of light and electron microscopy, restorative processes are studied in the transplanted muscles. Acceleration of histomorphogenesis of the muscular and nervous tissues is stated from the lower toward the higher Vertebrata. When the transplants are deprived of the connection with the nervous system, the cause of the form organization process in all the animals investigated is disturbed, however, the nervous-trophic regulation is of the greatest importance in the mammalia. The experiments reveal mutual regulation of the plastic activity in the nervous and muscular tissues, that becomes more intensive in the course of evolution.     

Cell volume maintenance and regulation in kidney tissues of various vertebrates

Ouabain-sensitive and ouabain-insensitive mechanisms are shown to participate to a different extent in the cell volume maintenance in kidney tissues of various vertebrates. The ouabain-insensitive mechanisms predominate in the lamprey and in fresh-water fishes, whereas in the flounder, representing sea fishes, there is a complete predominance of the ouabain-sensitive mechanism. In the rabbit kidney cortex tissue the two systems play a comparable role. Analogous inter-species differences are displayed when the cells regulate their volume in anisoosmolar media.