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The rate of pyruvate oxidation by mitochondria from blowfly flight muscle decreased in the presence of tris (hydroxymethyl) aminomethane (Tris). An increase in the rate of mitochondrial swelling was concomitant with the loss of pyruvate oxidation. These changes were prevented by bovine serum albumin, adenosine triphosphate, and magnesium ions, factors required for mitochondrial contraction. Proline, but not glutamate or malate, restored the rate of pyruvate oxidation to original values. These findings suggest that mitochondrial swelling leads to leakage of intramitochondrial intermediates of the Krebs cycle, accounting for the decrease in the rate of pyruvate oxidation. Exogenous proline penetrates the mitochondrial membrane and is rapidly oxidized, via glutamate, forming intramitochondrial precursors of oxaloacetate. Malate and glutamate were ineffective because of the selective permeability of the mitochondrial membrane.

Glycogen from flight muscle of the blowfly, Phormia regina, has been characterized ultrastructurally and biochemically . In situ, glycogen is in the form of rosettes, which vary in size with diameters of up to 0.1 µ . Sedimentation analysis of pure glycogen, isolated by mild buffer extraction, reveals a polydisperse molecular weight spectrum, with larger particles having molecular weights of 100 million . Treatment of native glycogen with alkali, under conditions usual for the extraction of the polysaccharide from tissues, results in a 5-to 10-fold reduction in molecular weight, as well as a chemical alteration of the molecule . Flight muscle phosphorylase has a lower affinity for native than for alkali-treated glycogen. The maximum velocity of the enzyme is also lower with native substrate . The apparent K. . for inorganic phosphate is higher with native glycogen as cosubstrate . These kinetic differences with native and partially degraded glycogen demonstrate the importance of using the natural substrate in studies of biochemical control mechanisms .When the blowfly initiates flight, an intense rate of glycogenolysis in the flight muscle is triggered (1) . The mechanisms of the control of glycogen utilization in the muscle is being studied . As part of this study, glycogen from blowfly flight muscle has been examined . This is of significance because of the observations that the physical and biological properties of the polysaccharide depend on the tissue of origin, the metabolic state of the tissue, and the method of extraction (2, 3) .Heretofore, glycogen from insects has not been characterized . In this paper, we report the isolation by mild buffer extraction of glycogen from flight muscle of the blowfly, Phormia regina, and describe its biophysical and biochemical properties. The polysaccharide has been found to be polydisperse, with a continuous spectrum of particle sizes up to 200 mµ, with the largest particles having molecular weights of 100 million . Marked differences in the kinetics of flight muscle phosphorylases with native and partially degraded glycogens, as substrates, indicate the importance of using native glycogen in studies of regulatory mechanisms . METHODS AND MATERIALS Raising of InsectsBlowflies, Phormia regina, were maintained in laboratory culture at 23'C and 12 hr of light per day . The larvae were reared on horsemeat, and the adult flies were fed powdered milk and sucrose . 7 days fol-