Comparative properties of three forms of glucose-6-phosphate dehydrogenase in Drosophila melanogaster

The effect of Zn2+ on glucose 6-phosphate dehydrogenase activity from Bufo arenarum toad ovary and alfalfa plants

The effect of Zn2+ on glucose 6-phosphate dehydrogenase (G6PD) activity was monitored in samples from Bufo arenarum toad ovary and alfalfa plants, in the search for a possible new bioindicator able to detect levels of exposure through contaminated soils, and also to elucidate possible similarities between the enzyme from animal and plant tissues. The in vivo effect was evaluated after exposure of the toads to the metal in Ringer solution during 30 days and after 10 days of treatment in 6 weeks old plants, cultured under laboratory conditions. In vitro effects were measured in different extracts from control samples and partially purified enzyme from ovarian tissue as well as in different extracts from control alfalfa plants, by addition of the metal to the reaction mixture containing the enzyme. G6PD from toad ovary was noncompetitively inhibited by zinc both in vivo and in vitro, under all the experimental conditions studied. A kinetic analysis of the enzyme activity showed that the Michaelis-Menten constant (Km) was not modified, while maximal velocity (Vmax) decreased as the consequence of treatment. It was not possible to obtain a dose-response curve for the effects of Zn2+ on G6PD from alfalfa whole plants, measured in vivo or in vitro. Only leaf extracts evidenced a possible relationship between treatment with the metal and G6PD activity alteration. The results agree with a possible role for G6PD as a biomarker of effect and exposure to Zn2+ in B. arenarum ovarian tissue but not in alfalfa plants.

Prospective and retrospective tests of evolutionary theories of senescence

Retrospective and prospective methods in the study of the evolution of longevity and senescence are compared. Retrospective studies can provide tests of evolutionary theories of senescence through the interpretation of evolutionary pattern demonstrated by species in nature. Patterns in longevity displayed by African rivulin fishes provide a clear and incisive example of the evolution of longevity and associated life history characters, but such tests are often difficult to find or unclear in the a posteriori interpretation of evolution that they offer. Far more experimentation of the prospective kind has been applied to testing theories of life span. Though prospective tests of evolutionary theory are compromised to a degree by the artificiality of the laboratory environment, experiments performed there are not necessarily invalid. In addition, prospective tests offer the added impetus that theoretical predictions are tested a priori. The use of Drosophila melanogaster as a laboratory model for the study of longevity has provided a number of particularly enlightening recent advances describing the number and distribution of genes controlling longevity, the metabolic pathways by which other characters are physiologically associated with life span, and even the controlling genetic elements affecting those traits. Improvements in longevity shown under programs of selective breeding may be the result of adaptations in the glycolytic pathway altering the ability to utilize the sugar sucrose as a food source.

The role of glucose-6-phosphate dehydrogenase in the evolution of longevity in Drosophila melanogaster

Different polymorphic elements of the enzyme glucose-6-phosphate dehydrogenase (G6PD) are favoured under selection for long versus short life span. Replicate independently selected populations of short-lived individuals exhibit a more rapidly migrating and less actively staining allozyme, while long-lived populations have a slower migrating and more active allozyme. These correspond to the common ZwA and ZwB variants of the G6PD locus Zw. In vitro measurements show G6PD activity varies with allozymes and life span. Long-lived males have 64 per cent greater activity in G6PD, while females of long-lived strains are 108 per cent higher than those of short-lived strains. Previous studies of these strains have repeatedly demonstrated additivity of life span in F1 crosses. Activity of G6PD in reciprocal F1 populations is additive and intermediate between parents.

Comparison of in vitro and in vivo activities associated with the G6PD allozyme polymorphism in Drosophila melanogaster

Earlier studies of the A and B allozymes at the G6pd locus show a differential ability of the genotypes to suppress the loss of viability associated with a low activity 6-phosphogluconate dehydrogenase mutation, 6Pgdlo1. This observation indicates a relatively lower activity for the A allozyme genotype, but it is not known if this level of suppression required a large difference in in vivo activity. To clarify this difference an analysis of the biochemical properties of the purified allozymes was carried out, as well as an analysis of the activity level associated with an original low activity P element-derived allele which had partially reverted and lost its suppression ability. G6PD activity and protein level were studied in 47 X chromosome lines from North America. The A genotype averages a 9% lower Vmax. From analysis of the correlation between G6PD activity and protein level it remains unclear whether the allozyme Vmax difference results from dissimilarity in protein level or kcat. At 25 degrees and physiological pH, comparative studies of the steady-state kinetics show the two purified allozyme variants differ significantly in their KM values for glucose-6-phosphate and NADP, and the K1 for NADPH. In aggregate these parameters predict the A genotype possesses a 20% lower in vitro catalytic efficiency. A partial revertant of a P element-derived low activity B variant, was shown to lose the ability to suppress 6Pgdlo1 low viability after acquiring only 60% of normal B activity. This last comparison shows the A genotype activity must be reduced in vivo by at least 40%.

Nucleotide sequence of the Drosophila glucose-6-phosphate dehydrogenase gene and comparison with the homologous human gene

Glucose-6-phosphate dehydrogenase (G6PD) has a major role in NADPH production and is found in almost all cell types. The structural gene for G6PD is X-linked in Drosophila melanogaster, as it is in most eukaryotic organisms, and due to its ubiquitous expression, it can be considered a typical 'housekeeping' gene. Here we present the complete nucleotide (nt) sequence of G6PD cDNAs as well as the genomic copy of the G6PD gene. The G6PD gene has three introns so that the protein-coding region is divided into four segments. The 5'-end of mature G6PD mRNA is located 289 +/- 1 nt upstream from the start codon. The sequence upstream from the transcription start point is G + T-rich and contains no commonly found transcription regulatory elements, such as a TATA box or GGGCGG sequence. D. melanogaster G6PD is 65% homologous with the human G6PD protein but has no homology with the human sequence for the first 42 amino acid residues. The G6PD gene was shown to be active when transduced to autosomal positions. For each transformant, G6PD activity in both male and female adults was not significantly different, indicating that the transduced gene, unlike the resident G6PD, is not dosage-compensated in males.