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1. 1. Four protein fractions with ATPase activity have been obtained from cockroach thoracic muscle mitochondria. 2. 2. Purifications of forty- to one hundredfold were achieved using ultracentrifugarion, (NH 4 ) 2 SO 4 fractionation and column chromatography on Sephadex and on DEAE cellulose. 3. 3. ATPase IV appears to be specific for purine nucleoside triphosphates, while the other three dephosphorylate purine and pyrimidine nucleoside di- and triphosphates. ATPase I degrades nucleoside monophosphates. Evidence on the cold lability of the four enzymed is also presented. 4. 4. These results are discussed in relation to the ability of insect sarcosomes to degrade ATP.

1. 1. Myokinase (ATP-AMP phosphotransferase) was isolated from thoracic muscle mitochondria of the American cockroach, Periplaneta americana (L.). 2. 2. The enzyme was purified greater than 100-fold by ammonium sulfate fractionation and column chromatography on Sephadex. 3. 3. The purified enzyme requires magnesium, but exhibits some activity in the presence of manganese or calcium. It is specific for the adenosine nucleotides, and has a pH optimum of 5.8–6.0 depending upon buffer. 4. 4. The reaction is markedly inhibited by fluoride at 2 × 10 −2 M. K m values 3.1 × 10 −4 , 1.5 × 10 −3 and 3.2 × 10 −4 M were obtained for ATP, ADP and AMP, respectively. 5. 5. The equilibrium constant was calculated to be 0.44 in the presence of magnesium. 6. 6. The significance of this enzyme in the metabolism of adenosine nucleotides in insects is discussed.

1. 1. Crude tissue supernatants from the thoraces and abdomens of the American cockroach have been shown to contain numerous nucleotide metabolizing enzymes. 2. 2. These enzymes include four which metabolize pyrimidine compounds: nucleoside triphosphatase, 5′-nucleotidase, nucleoside deaminase and uridine phosphorylase. 3. 3. Ammonium sulfate fractionation of the supernatants has resulted in low-level purification and some degree of separation of each of these activities. 4. 4. The properties of these enzymes, such as substrate specificity, pH optima, etc., have been investigated. 5. 5. A tentative partial pathway for pyrimidine catabolism has been proposed for this insect.