The -glycerophosphate cycle in Drosophila melanogaster. I. Biochemical and developmental aspects

Maintenance mechanism of polymorphism at the alpha-Gpdh locus in Drosophila melanogaster

Polymorphism at the alpha-Gpdh locus was studied in Drosophila melanogaster. Using two different lines, one marked by the F allele (FF line) another by the S allele (SS line), four populations were initiated, two in which the initial frequency of F was 0.1 and two in which it was 0.9. They have been observed for 34 generations. From the fifth generation on, the equilibrium frequency in the four cages was about 0.60. Viability has been measured during the evolution of te populations while F frequencies changed and recombinations between the FF and SS lines occurred. It has been evaluated in synthetic populations built with different frequencies: (1) from the original FF and SS lines and (2) from FF and SS lines extracted after 34 generations of joint evolution. In all three cases, the FF viability depended on the frequency of the F allele. The similarity of the three linear regressions implies that alpha-Gpdh locus or other closely linked loci is the target of the selection in the populations analyzed here.

Adaptation of Drosophila enzymes to temperature. III. Evolutionary conservation in mitochondrial enzymes

The evolutionary behavior of two mitochondrial enzymnes (L-glycerol 3-phosphate:cytochrome c oxidoreductase E.C.1.1.1.95, alpha GPO, and L-malate: NAD+ oxidoreductase, E.C.1.1.1.37, m-MDH) obtained from several temperate and tropical Drosophila species was examined by comparing their catalytic properties, which related to temperature (Km-Ea-Q10-Thermostability). Mitochondrial alpha GPO or m-MDH obtained either from template or from tropical species was found to exhibit similar catalytic properties while for both cytosolic enzymes, the alpha GPDH and s-MDH, Km patterns were similar among species from the same thermal habitat and different thermal habitats. In combination with other observations reported in the literature these facts support the view that the function, and probably the structure, of mitochondrial enzymes are better conserved in evolution than those of the corresponding enzymes found in the cytosol. It is proposed that the relative invariance of the mitochondrial enzymes structure is probably linked to a necessary relative invariance of molecular interactions inside the mitochondrion.

Functional significance of amylase polymorphism in Drosophila melanogaster. III. Ontogeny of amylase and some alpha-glucosidases

Changes in amylase (E.C. 3.2.1.1), maltase (E.C. 3.2.1.20), sucrase, and PNPGase activities in relation to changes in wet weight and protein content were studied during the development of larvae and adult flies from two strains of Drosophila melanogaster, homozygous for different amylase alleles. All alpha-glucosidase activities increase exponentially during a large part of larval development, parallel to the increase in weight, and drop at the end of the third instar. Amylase activity of the Amy1 strain follows the same pattern. In contrast, amylase activity of the Amy4,6 strain continues its exponential increase longer. In the third larval instar amylase activity in the Amy4,6 strain becomes much higher than in the Amy1 strain. During the first hours of adult life amylase activity of the two strains does not differ. Then Amy4,6 activity starts to rise and becomes much higher (4-5 times) than Amy1 amylase activity, which remains approximately constant. All adult enzyme activities are much higher than in larvae. Comparison of enzyme activity of amylase and alpha-glucosidases in larvae and adults confirms that differences in amylase activities can become important only when starch is a limiting factor in the food.

Quantitative subunit hybridization of drosophila alpha-glycerophosphate dehydrogenase

The dimeric enzyme, alpha-Glycerophosphate dehydrogenase, was purified from eight Drosophila species by the method of Collier et al. (1976). The enzymes were inactivated at high pH and the conditions sufficient for reactivation were established. Electrophoretic patterns of reactivated alpha-glycerophosphate dehydrogenases which were mixed following inactivation of two species' enzymes, demonstrate that high pH dissociates the enzyme into its constituent subunits and reactivation involves subunit reassociation. Twenty interspecific combinations of dissociated enzymes were allowed to reassociate, and the amounts of both heterospecific and homospecific enzyme activity and protein were determined by densitometry. In all 20 tests there were no differences between observed and expected heterospecific:homospecific enzyme ratios. These results are consistent with the very slow rate of evolution of this enzyme in the family Drosophilidae (Collier and MacIntyre, 1977).

Purification and properties of the major isozymic form of cytoplasmic glycerol-3-phosphate dehydrogenase from rabbit liver

The major isozymic form of sn-glycerol-3-phosphate dehydrogenase (sn-glycerol-3-phosphate:NAD+ 2-oxidoreductase, EC 1.1.1.8) has been purified from rabbit liver using a simplified three-step chromatographic procedure involving an ion exchange and two affinity chromatography steps. The 1200-fold purified enzyme is electrophoretically homogeneous, nucleotide-free, and possesses a specific activity of 295 units/mg and an isoelectric point of 6.5. A steady-state kinetic analysis was applied to both the forward and reverse reactions. The NADH oxidation reaction was found to adhere to Michaelis-Menten behavior with Km values of 22 micrometer and 75 micrometer for NADH and dihydroxyacetone phosphate, respectively. In the NAD reduction reaction, sigmoidal kinetic patterns were observed when NAD was the variable substrate whereas with sn-glycerol-3-phosphate as the variable substrate, strictly hyperbolic kinetics were observed. The apparent Km values for NAD and glycerol-3-phosphate were 83 and 909 micrometer, respectively. By comparison with published reports, these results demonstrate that the rabbit muscle and liver isozymes of sn-glycerol-3-phosphate dehydrogenase have different kinetic properties and suggest that the liver isozyme is better adapted to participation in glyconeogenesis in vivo.

Heat stability studies at the alpha-glycerophosphate dehydrogenase locus in populations of Drosophila melanogaster

The level of hidden variation in populations of Drosophila melanogaster at the Gpdh+ locus was determined by thermal stability studies of the protein. The results indicate a lack of variation using these methods both in and between the two common electrophoretic variants. It is suggested that alpha-GPDH is conserved in primary structure, which may be related to its critical role in flight muscle metabolism.

Age-dependent alpha-glycerophosphate dehydrogenase activity changes in mutant and wild type Drosophila melanogaster

The age-related changes in the activity of the extramitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPDH) were compared in two mutants of Drosophila melanogaster, a vestigial-winged and an alpha-glycerophosphate dehydrogenase deficient mutant with that of the wild type. The age-dependent patterns of activity change in both mutants were shown to be identical to that of the wild type. This is in spite of the lack of flight ability in both mutants, the reduced enzyme activity levels in the alpha-glycerophosphate mutant, and in the case of the vestigial flies, of reduced life-span. The results suggest that those mechanisms responsible for the observed aged-related activity changes in alpha-GPDH are intrinsically regulated, independent of functional flight, genetic alteration of specific activity, and life-span.

Origin of alpha-glycerophosphate dehydrogenase isozymes in Drosophila melanogaster and their functional relationship in the alpha-glycerophosphate cycle

The basis for the differentiation of L-glycerol-3-phosphate dehydrogenase (alpha-GPDH) into larval and adult isozymes in Drosophila melanogaster was investigated by the correlation of a lack of appearance of each isozyme during development within Drosophila bearing alpha-GPDH "null" alleles and by the study of a putative conversion factor. Conversion studies indicate the presence of a heat-labile RNase-resistant conversion factor present in crude larval extracts with the ability to convert GPDH-1 to GPDH-2 and GPDH-3 but not vice versa. In addition, "null" mutations at the Gpdh locus obliterate all isozymatic species of alpha-GPDH in all developmental stages. These observations suggest that all alpha-GPDH isozymes are the product of a single structural gene and that the multiple forms of this enzyme arise during successive developmental stages through an epigenetic modification of the primary Gpdh+ polypeptide. Finally, observations are reported which bear on the functional divergence of the alpha-glycerophosphate cycle in the adult and larval stage of development.

Genetic control of soluble NAD-dependent sorbitol dehydrogenase in Drosophila melanogaster

Experiments utilizing standard techniques of cell fractionation and disc electrophoresis have revealed the presence of three distinctly different enzymes which catalyze the oxidation of D-sorbitol in crude extracts of Drosophila melanogaster adults. These include (1) a soluble NAD-dependent sorbitol dehydrogenase (NAD-SoDHS), (2) a mitochondrial NAD-dependent sorbitol dehydrogenase (NAD-SoDHm), and (3) a soluble NADP-dependent sorbitol dehydrogenase (NADP-SoDH). The structural gene for NAD-SoDHS has been mapped to a locus between 65.3 and 65.6 on the third chromosome by means of an electrophoretic variant and a low-activity allele. Through the use of segmental aneuploidy, this gene has been localized to the region limited by salivary bands 91B-93F. Because mutants which alter either the activity or electrophoretic effect on the mitochondrial or NADP-dependent forms, it is suggested that the enzymes in this system are coded for autonomously by different genes.

Screwworm eradication: inadvertent selection for noncompetitive ecotypes during mass rearing

The rapid fixation of a rare allelic form of alpha-glycerol phosphate dehydrogenase is related to a loss of competitive ability in nature of factory-reared screwworm flies. The increase in frequency results from selection for survival under conditions of domestication and rapid development at high constant temperatures in the factory.

Evidence for the adaptive significance of enzyme activity levels: interspecific variation in alpha-GPDH and ADH in Drosophila

The activity levels of alcohol dehydrogenase and alpha-glycerophosphate dehydrogenase were compared among nine species of Drosophila representing three phylogenetic groups. For any given life stage , interspecific variability in activity level was much greater for ADH than for d-GPDH. Patterns of ontogenetic expression of enzyme activity were also much more variable among species for ADH than for alpha-GPDH. These results are consistent with the interpretation that alpha-GPDH is involved with a relatively uniform adaptive function among species, whereas ADH levels may reflect variable adaptive capabilities. There is a significant correlation between ADH activities and survivorship on alcohol-treated media for these nine species.

Polymorphism at the alpha-glycerophosphate dehydrogenase locus in Drosophila melanogaster. I. Properties of adult allozymes

A biochemical comparison was made between alpha-glycerophosphate dehydrogenase allozymes from Drosophila melanogaster. Enzymes extracted from the three major genotypes were indistinguishable in terms of their pH optima and thermal stabilities. Distinctive differences were observed for three parameters; temperature dependence of specific activity, temperature dependence of K-m, and reaction rate constancy over a physiological temperature range. These results are discussed in terms of a model of balancing selection and the existence of spatial and temporal allele frequency clines in natural populations.

The alpha-glycerophosphate cycle in Drosophila melanogaster. IV. Metabolic, ultrastructural, and adaptive consequences of alphaGpdh-l "null" mutations

"Null" mutations previously isolated at the alphaGpdh-1 locus of Drosophila melanogaster, because of disruption of the energy-producing alpha-glycerophosphate cycle, severely restrict the flight ability and relative viability of affected individuals. Two "null" alleles, alphaGpdh-1(BO-1-4), and alphaGpdh-1(BO-1-5,) when made hemizygous with a deficiency of the alphaGpdh-1 locus, Df(2L)GdhA, were rendered homozygous by recombination with and selective elimination of the Df(2L)GdhA chromosome. After over 25 generations, a homozygous alphaGpdh-1(BO-1-4) stock regained the ability to fly despite the continued absence of measurable alphaGPDH activity. Inter se heterozygotes of three noncomplementing alphaGpdh-1 "null" alleles and the "adapted" alphaGpdh-1(BO-1-4) homozygotes were examined for metabolic enzymatic activities related to the energy-producing and pyridine nucleotide-regulating functions of the alpha-glycerophosphate cycle in Drosophila. The enzyme functions tested included glyceraldehyde-3-phosphate dehydrogenase, cytoplasmic and soluble malate dehydrogenase, lactate dehydrogenase, mitochondrial NADH oxidation, oxidative phosphorylation, and respiratory control with the substrates alpha-glycerophosphate, succinate, and pyruvate. These activities in any of the mutant genotypes in early adult life were indistinguishable from those in the wild type. There was, however, a premature deterioration and atrophy of the ultrastructural integrity of flight muscle sarcosomes observed by electron microscopy in the "null" mutants. These observations were correlated with a decrease in state 3 mitochondrial oxidation with alpha-glycerophosphate, succinate, and pyruvate, as well as with loss of respiratory control in adults as early as 2 wk after eclosion. Such observations, which normally are seen in aged dipterans, were accompanied by premature mortality of the mutant heterozygotes. The adapted alphaGpdh-1(BO-1-4) was identical with wild type in each of the aging characters with the single exception of lowered rates of mitochondrial oxidative phosphorylation.