Isolation and Characterization of Glycerol-3-Phosphate Dehydrogenase-Defective Mutants of \u3cem\u3eNeurospora crassa\u3c/em\u3e

Three glycerol-nonutilizing mutants deficient in the mitochondrial glycerol-3-phosphate (G3P) dehydrogenase (EC 1.1.99.5) were isolated from inlts derivatives of Neurospora crassa following inositolless death at elevated temperatures on minimal glycerol medium. These mutants failed to grow on glycerol as a sole carbon source, but could grow on acetate, glucose, or mannitol media and were female fertile in genetic crosses, thereby distinguishing them from the previously reported polyol-protoperithecial defective Neurospora mutants. In addition, these glp mutants exhibited a distinct morphological alteration during vegetative growth on sucrose slants and colonial growth on sorbose-containing semicomplete medium. The glp-2 locus was assigned a location between arg-5 and nuc-2 on chromosome IIR on the basis of two-factor crosses and by duplication coverage by insertional translocation ALS176, but not NM177. All mutations were allelic as judged from the absence of both complementation in forced heterokaryons and genetic recombination among glp-2 mutations. The reversion frequency of all three mutations was less than 1010, indicating probable deletions in these strains. No G3P dehydrogenase activity could be detected in either cytosolic or mitochondrial extracts from mutant strains grown on glycerol, glucose, or galactose media. These results suggest that the glp-2 locus may be the structural gene for both the cytosolic and mitochondrial forms of G3P dehydrogenase or for a cytosolic precursor of the mitochondrial G3P dehydrogenase. The defect is specific for the G3P dehydrogenase since normal activities of the mitochondrial cytochrome oxidase and succinate dehydrogenase and the cytosolic glycerol dehydrogenase and dihydroxyacetone phosphate reductase are detected in mutant extracts. During attempted growth of glp-2 mutants on glycerol media, there was an accumulation of G3P in culture filtrates, a reduction in the mycelial growth rate, and a decreased level of glycerokinase induction

Effects of Thyrotoxicosis on Mitochondrial Enzymes of Rat Soleus

Cytochrome oxidase, glycerol-3-phosphate dehydrogenase, and succinate dehydrogenase were measured in mitochondrial fractions obtained from rat soleus muscle of control and 8 week T3 + T4 treated animals. Under these conditions of prolonged treatment, there is a five-fold increase in the specific activities of both cytochrome oxidase and glycerols-3-phosphate dehydrogenase. Significant increases in total cellular mitochondrial content and enzyme activities were observed in T3 + T4 treated animals as compared to controls. These results indicate that thyrotoxicosis can induce selective changes in mitochondrial enzymes in slow twitch red (Type I) muscle fibers

Muscle Fatigue with Prolonged Exercise: Contractile and Biochemical Alterations

Alterations in the contractile and biochemical properties of fast and slow skeletal muscle were studied in rats following a prolonged swim to exhaustion. The exercise produced glycogen depletion (less than 1 mg/g tissue) in muscles representative of all three fiber types; the isometric contractile properties were altered in the 84% type I soleus (SOL) and the 60% type IIa extensor digitorium longus (EDL) but not in the 100% type IIb superficial region of the vastus lateralis (SVL). Peak tetanic tension (Po) and the rate of tension development and decline all decreased after prolonged exercise in both the SOL and the EDL. The maximal isotonic shortening velocity was highly correlated with the myofibrillar ATPase activity, and both were relatively resistant to fatigue. Furthermore, the Ca2+ sensitivity of the myofibrils was unaffected by exercise in both fast and slow muscle. The Ca2+ uptake capacity of the sarcoplasmic reticulum (SR) was reduced in both the SOL and the fast-twitch type IIa deep region of the vastus lateralis, whereas the SR ATPase activity was unchanged. Our findings provide evidence that prolonged exercise produces alterations in contractile and biochemical properties of type I and IIa but not type IIb fibers and that muscle fatigue as measured by a decline in Po is not necessarily correlated with glycogen depletion

Effect of Moderate Daily Exercise on Acute Glomerulonephritis

Exercise can induce proteinuria, hematuria and cylindruria in normal individuals. This suggests that exercise adversely affects glomerular function. In this study we examined the impact of moderate daily treadmill exercise on the glomerulonephritis (GN) of ‘one-shot” bovine serum albumin (250 mg/kg i.v.) serum sickness in rabbits. We found that exercise alone increased serum creatinine concentration (Scr) but exercise plus GN did not increase Scr further. Blood urea nitrogen values were unchanged. Albuminuria and the renal histopathology findings were not different between the exercised and non-exercised groups of rabbits. Muscle cytochrome oxidase and mitochondrial protein concentrations were not increased in the exercised animals. We conclude that exercise, below the level that causes exercise adaptation in muscle enzymes, does not adversely affect this form of acute GN