Models of seasonal growth of the equatorial carp Labeo dussumieri in response to the river flood cycle

Synopsis The phenology of Labeo dussumieri, an omnivorous carp common to South Asia, was investigated in a population inhabiting a flood plain anabranch of the Mahaweli Ganga, Sri Lanka. The Mahaweli Ganga exhibited a bimodal discharge pattern typical of many equatorial rivers, with a minor peak during the S.W. monsoon and a major peak during the N.E. monsoon. Seasonal changes in several lotic variables were measured in an attempt to correlate changes in environmental conditions to reproduction and growth in L. dussumieri. The onset of gonad recrudescence and spawning were synchronized with the increased river discharge during the S.W. and N.E. monsoons: gonad development followed one monsoonal discharge peak and spawning took place at the beginning of the other. Most fish spawned at the beginning of the major discharge peak in October and November, following the September dry season. Increased discharge was concomitant with a fall in temperature, light intensity, pH and conductivity. Growth was shown to be seasonal, exhibiting an annual bimodal pattern with peaks coincident with S.W. and N.E. monsoonal rains. Seasonal changes in growth were expressed by two models in terms of: (a) change of somatic weight or fork length with time, (b) change of specific growth rate in response to river discharge, modified by somatic weight. Gonad recrudescence and spawning stress did not appear to influence growth rate.     

Physiological roles of animal succinate thiokinases Specific association of the guanine nucleotide-linked enzyme with haem biosynthesis

The discovery of two distinct succinate thiokinases in mammalian tissues, one (G-STK) specific for GDP/GTP and the other (A-STK) for ADP/ATP, poses the question of their differential metabolic roles. Evidence has suggested that the A-STK functions in the citric acid cycle in the direction of succinyl-CoA breakdown (and ATP formation) whereas one role of the G-STK appears to be the re-cycling of succinate to succinyl-CoA (at the expense of GTP) for the purpose of ketone body activation. A third metabolic participation of succinyl-CoA is in haem biosynthesis. This communication shows that in chemically induced hepatic porphyria, when the demand for succinyl-CoA is increased, it is the level of G-STK only which is elevated, that of A-STK being unaffected. The results implicate G-STK in the provision of succinyl-CoA for haem biosynthesis, a conclusion which is further supported by the observation of a high G-STK/A-STK ratio in bone marrow.     

Studies on well-coupled Photosystem I-enriched subchloroplast vesicles — energy-dependent switching between two different active states of the proton-translocation adenosine triphosphatase

Single-turnover flash-induced ATP synthesis coupled to natural cyclic electron flow in Photosystem I-enriched subchloroplast vesicles (from spinach) was continuously followed by the luciferin-luciferase luminescence. The ATP yield per flash was maximal (1 ATP per s per 1000 Chl) around a flash frequency of 0.5–2 Hz. It decreased both at lower and higher flash frequencies. The decrease at high flash frequency was due to limitation by the electron-transfer rate, while the decrease at low flash frequency was directly due to intrinsic properties of the ATPase itself. Carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP) decreased the yield at low frequency more than at high frequency. The same behaviour was observed if electron transfer was artificially mediated by pyocyanin. If the ADP concentration was increased from 40 to at least 80 μM, or if the vesicles were preincubated with 5 mM dithiothreitol (DTT), the decrease of the yield at flash frequencies below 0.5 Hz was no longer observed. Incubation with DTT increased the rates of ATP hydrolysis and synthesis at any flash frequency. The decrease of the yield could be elicited again by addition of 50 nM FCCP. It is concluded that at low levels of the protonmotive force (Δ gm_H⁺), the ATPase is converted into an active ATP-hydrolyzing state in which ATP synthesis activity is decreased due to a decreased affinity towards ADP and/or to a decreased release of newly synthesized ATP, that can be cancelled by increasing the ADP concentration or by addition of DTT in the absence of uncoupler.     

Genetical and biochemical comparisons of alcohol dehydrogenase isozymes from Anastrepha fraterculus and A. obliqua (Diptera: Tephritidae): Evidence for gene duplication

The electrophoretic patterns of the enzyme alcohol dehydrogenase (ADH) from Anastrepha fraterculus and A. obliqua were studied. Two loci were found to code for the enzyme in A. fraterculus, and three in A. obliqua. In both species, all isozymes were active in third-instar larvae. A cationic isozyme (Adh-1) was active mainly in the visceral fat body of both species. In A. fraterculus, the locus had an anionic polymorphic isozyme (Adh-3) that was detected in the parietal fat body. In addition to these two loci, a third locus for an anionic isozyme (Adh-2), which was active in the digestive tube of larvae, was present in A. obliqua and probably resulted from gene duplication. For both species, multiple forms of the isozymes are formed by binding of an NAD-carbonyl compound, as in Drosophila melanogaster. Both larvae and early pupae of A. obliqua had almost twice the specific ADH activity as A. fraterculus. The ethanol content of the host fruit infested with A. obliqua (red mombim) was also higher than that of the host fruit infested with A. fraterculus (guava).This research was supported by grants from Conselho Nacional de Desenvolvimento Científico e Tecnologico (CNPq-PIG 40.2486/82).     

Restriction endonuclease mapping of ribosomal RNA genes: Sequence divergence and the origin of the tetraploid treefrog Hyla versicolor

Hyla chrysoscelis (2n=24) and H. versicolor (2n=48) are a diploid-tetraploid species pair of treefrogs. Restriction endonuclease mapping of ribosomal RNA (rRNA) gene repeat units of diploids collected from eastern and western populations reveals no differences within rRNA gene coding regions but distinctive differences within the nontranscribed spacers. A minimum of two physical maps is required to construct an rRNA gene map for the tetraploid, whose repeat units appear to be a composite, with about 50% of the elements resembling the western diploid population and about 50% resembling the eastern population. These results imply that this population of the tetraploid species may have arisen from a genetically hybrid diploid. Alternatively, the dual level of sequence heterogeneity in H. versicolor may reflect some type of gene flow between the two species. The coding region of the rRNA genes in the tetraploid differs from that in either diploid in about 20% of all repeat units, as exemplified by a BamHI site located near the 5 terminus of the 28 S rRNA gene. If the 20% variant class of 28 S rRNA gene coding sequences is expressed, then there must be two structural classes of ribosomes; if only the 80% sequence class is expressed, then a genetic control mechanism must be capable of distinguishing between the two different sequence variants. It is postulated that the 20% variant sequence class may be correlated with a partial functional diploidization of rRNA genes in the tetraploid species.This research was supported, in part, by NSF Grants CDP-8002341 and PRM-8106947 and by faculty research grants from Miami University to J.C.V.     

Developmental Pattern for Phosphatidylserine Decarboxylase in Rat Brain

In adult rats, a significant portion of brain ethanolamine glycerophospholipids are synthesized by a pathway involving phosphatidylserine decarboxylase, a mitochondrial enzyme. We have now examined whether this enzyme plays a particularly prominent role during development. Activities for both phosphatidylserine decarboxylase and succinate dehydrogenase (another mitochondrial enzyme) were determined in brain homogenates from rats 5 days of age to adulthood. Succinate dehydrogenase activity, expressed on a per unit brain protein basis, increased markedly during development. This pattern has been reported previously and is as expected from the postnatal increase in oxidative metabolism. In contrast, phosphatidylserine decarboxylase activity decreased 40% from 5 to 30 days of age. The apparent Km for brain phosphatidylserine decarboxylase was 85 microM in both young (8- and 20-day-old) and adult animals. Parallel studies in vivo were carried out to determine the contribution of the phosphatidylserine decarboxylase pathway, relative to pathways utilizing ethanolamine directly, to the synthesis of brain ethanolamine glycerophospholipids. Animals were injected intracranially with a mixture of L-[G-3H]serine and [2-14C]ethanolamine and incorporation into the base moieties of the phospholipids determined. The 3H/14C ratio of ethanolamine glycerophospholipids decreased about 50% during development. Our studies in vitro and in vivo both suggest that phosphatidylserine decarboxylase plays a significant role in the synthesis of brain ethanolamine glycerophospholipids at all ages, although it is relatively more prominent early in development.     

A minimum mechanism for Na+−Ca++ exchange: Net and unidirectional Ca++ fluxes as functions of ion composition and membrane potential

Summary Both simultaneous and consecutive mechanisms for Na⁺–Ca⁺⁺ exchange are formulated and the associated systems of steady-state equations are solved numerically, and the net and unidirectional Ca⁺⁺ fluxes computed for a variety of ionic and electrical boundary conditions. A simultaneous mechanism is shown to be consistent with a broad range of experimental data from the squid giant axon, cardiac muscle and isolated sarcolemmal vesicles. In this mechanism, random binding of three Na⁺ ions and one Ca⁺⁺ on apposing sides of a membrane are required before a conformational change can occur, translocating the binding sites to the opposite sides of the membranes. A similar (return) translocation step is also permitted if all the sites are empty. None of the other states of binding can undergo such translocating conformational changes. The resulting reaction scheme has 22 reaction steps involving 16 ion-binding intermediates. The voltage dependence of the equilibrium constant for the overall reaction, required by the 31 Na⁺Ca⁺⁺ stoichiometry was obtained by multiplying and dividing, respectively, the forward and reverse rate constants of one of the translocational steps by exp(–FV/2RT). With reasonable values for the membrane density of the enzyme (120 sites m²) and an upper limit for the rate constants of both translocational steps of 10⁵·sec^–1, satisfactory behavior was obtainable with identical binding constants for Ca⁺⁺ on the two sides of the membrane (10⁶ m ^–1), similar symmetry also being assumed for the Na⁺ binding constant (12 to 60m ^–1). Introduction of order into the ion-binding process eliminates behavior that is consistent with experimental findings.