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Mitochondria from flight muscle of aging blowflies, Phormia regina, were examined morphologically and biochemically with the electron microscope . An age-dependent degeneration of the mitochondria that is characterized, in part, by the reorganization of the inner membrane into myelin-like whorls has been found . The concentric rings increase in size and number, eventually replacing the normal cristal conformation . Glycogen rosettes are frequently seen in the center of the whorl and may represent the intrusion into the mitochondria of the glycogen in the cytoplasmic matrix of the muscle . The degenerating mitochondria are not associated with lysosomal activity, as indicated by the absence of acid phosphatase . An intense acid phosphatase activity is noted, however, in the dyad, comprising elements of the T system and sarcoplasmic reticulum . Cytochrome oxidase is active in the ultrastructurally intact portion of the mitochondrion but activity is not evident in that part of the mitochondrion that has undergone morphological change . Thus, the ultrastructural degradation of the mitochondria is correlated with a decrease in biochemical function . This suggests a correspondence between a decrease in the bioenergetic capacity of the flight muscle and a decline in the ability of the aged insect to fly .In pioneering experiments, Williams et al . (1) reported that the flight ability of flies declines markedly with age . The mechanism of this deterioration with senescence remains essentially unknown . Our previous studies on the control of intermediary metabolism in flight muscle (2-4) prompted us to examine whether the bioenergetic processes in this horrendously active tissue undergo changes during aging . Notable differences in the ultrastructure and biochemical activity of the muscle from young and old blowflies, Phormia regina, have now been found . In this paper, degenerative alterations in mitochondria with age, as determined by electron microscopy, are reported. METHODSBlowflies were maintained in laboratory culture as reported previously (5) . The flight muscles from female flies, 7-46 days old, were used . Mitochondria were isolated as described earlier (6) ; the isolation medium consisted of 0.15 M KCI, 0 .01 M Tris chloride, 1 mm ethylenediaminetetraacetate (EDTA), and 0 .5% bovine serum albumin, adjusted to pH 7 .4 .Unless noted otherwise, flies were bisected by a medical cut with a razor blade in ice-cold fixative containing 2 .5% glutaraldehyde, 0 .05 M cacodylate buffer, pH 7.4, and 0 .18 M sucrose (7) . Samples of muscle, less than 1 mm 3, were kept in fixative, at 0-4°C, for 3 hr and washed overnight in the cold with 0 .05 M cacodylate in 0 .3 M sucrose . The tissue was transferred to cold 1 % osmium tetroxide in 0 .1 M phosphate buffer, pH 7 .4, for 2 hr, dehydrated in an ethanol series, and embedded via propylene oxide in Epon 812 . Sections were cut with a diamond knife on an LKB Ultrotome III and mounted on 300-mesh copper grids. The specimens were stained with saturated uranyl acetate and l...

ABSTRACT"Null" mutations previously isolated at the aGpdh-1 locus of Drosophila rnelanogaster, because of disruption of the energy-producing a-glycerophosphate cycle, severely restrict the flight ability and relative viability of affected individuals.Two "null" alleles, aGpdh-18°-1-4, and otGpdh-1 ~°-~-5, when made hemizygous with a deficiency of the aGpdh-I locus, Df(2L)Gdh,4, were rendered homozygous by recombination with and selective elimination of the Dfl2L)GdhA chromosome. After over 25 generations, a homozygous aGpdh-1 ~°-1-4 stock regained the ability to fly despite the continued absence of measurable aGPDH activity. Inter se heterozygotes of three noncomplementing aGpdh-1 "null" alleles and the "adapted" aGpdh-1 B°-'-~ homozygotes were examined for metabolic enzymatic activities related to the energy-producing and pyridine nucleotide-regulating functions of the o~-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 a-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 a-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 aGpdh-I B°-14 was identical with wild type in each of the aging characters with the single exception of lowered rates of mitochondrial oxidative phosphorylation.