Cell Structure and the Metabolism of Insect Flight Muscle

Abstract

The biochemical properties of housefly flight muscle have recently been investigated to ascertain the mechanisms whereby energy is made available for the contractile processes (Sacktor, , a and b, 1954. These observations demonstrated the complete oxidation of some citric acid cycle intermediates in the sarcosomes (mitochondria) of these muscles, and showed that this oxidation could be coupled with synthesis of the energy-rich phosphate bonds in ATP. 1 Notwithstanding the multitude of enzymes in the mitochondrion, it was reported that isolated ssrcosomes were unable to oxidize glycogen and glucose (Levenbook, 1953, andSacktor, 1954). Since several experimenters had shown that these compounds are the main substances utilized during flight of flies (of. Chadwick, 1953), it appeared that extrasarcosomal enzymatic activities, too, were concerned with flight metabolism. This viewpoint was also inferred from previous results , which demonstrated a parallel in the distribution of certain enzymatic properties and the three prime morphological particulars of the flight muscle; namely, fibrils, sarcosomes, and sarcoplasm (the matrix that engulfs both fibrils and sarcosomes). Additional evidence for the localization of enzymes within these morphological entities and the relationship between them in the over-all metabolism of the flight muscle is provided in the present study. E X P E R I M E N T A L Fractionation ProceduresHouseflies, Musca domestic, a, of mixed sexes were used. These were reared and maintained by the procedure described previously (Sacktor, 1950).Flight muscle homogenates were prepared by grinding isolated thoraces in cold 0.9 per cent KCI with a Potter-Elvehjem homogenizer for 1 minute. The brei was then filtered through several layers of cheese-cloth to remove pieces of cuticle. The volume of the filtrate was adjusted with additional KC1 so that the final suspension contained the equivalent of 25 thoraces per ml. (10 to 15 rag. dry weight per ml.).The soluble and particulate fractions were obtained by centrifuging muscle homogenates, in the cold, for 10 minutes at about I0,000 g. The first supernatant was collected and used as 1 The following abbreviations will be used: ATP, adenosinetriphosph&te; ADP, adenosinediphosphate; AMP, adenosinemonophosphate; DPN, diphosphopyridine nucleotide; TPN, triphosphopyridine nucleotide.

An electron‐microscopic study of flight muscle development in the blowfly Lucilia cuprina

“…At the same time the oxygen consumption rises rapidly (Finch & Birt, 1962), the amounts of adenosine triphosphate (ATP) and arginine phosphate (both of which are present almost entirely in the thorax) increase considerably (Crompton & Birt, 1967), and the thoracic mitochondria are capable of reducing nicotinamide-adenine dinucleotide (Birt, 1966). Despite the evidence that blowfly mitochondria are incapable of oxidising fatty acids (Sacktor, 1955), all these data point to the utilization of fatty acids for the provisions of ATP by oxidative phosphorylation. This conclusion is supported by the demonstration (D'Costa & Birt, 1967) of a carnitine-dependent system capable of oxidizing fatty acids which can be detected in thoracic mitochondria isolated from pharate adults and from flies up to 4 days after emergence.…”

Metabolic pathways inAnopheles stephensimitochondria

“…Later studies demonstrated that the citric acid cycle was operational in sarcosomes of the housefly Musca domestica [3–7] and of the blowfly Phormia regina [8]. In general, oxidation was accompanied by the esterification of inorganic phosphate [3–7]. Specific patterns of oxidation were explored in the mitochondrial and supernatant fractions of the honey bee Apis mellifera [9].…”

Comparative Physiology: Fuel of Muscle Metabolism

“…Suffice it, then, to say here that a phosphorylative glycolytic pathway similar to that in vertebrate tis!lUe has been found in the housefly Musca domestica (58,73), the cockroach Periplaneta americana (74), the pea aphid Macrosiphum pisi (75), and the Bilkworm Bombyx mori (76). The pentose phosphate pathway has been clearly established in housefly tissues (77 to 79), and a similar pathway exists in the pea aphid (75) and the silk worm (76).…”

“…Weis-Fogh (66) showed that the average flight per formance in the locust required much more energy than was contained in the wing muscles and that flight depended on the large scale mobilization of fuel from the fat body. Sacktor (58) suggested that fats may be converted to acetate in the fat body which would then be transported to the tissue and oxidized via the TeA cycle. This suggestion has received some support from the observation (74) that in the muscle of Periplaneta, butyrate was not oxidized but acetate was rapidly consumed.…”

“…or 13.6 X 10-6 mg. per stroke. In an exhaustive study of the metabolism of housefly (Musca domestica) flight muscles, Sacktor (58) found that ho mogenates of these tissues vigorously oxidized carbohydrates but were un able to oxidize added fatty acids. This suggested that in this insect also, gly cogen provides the major vehicle for storage of flight energy.…”