Thermal enzymes. IV. Partial separation of an adenosinetriphosphatase from an apyrase fraction

Adenosine triphosphatase in isolated membranes of Staphylococcus aureus

The preparation of cytoplasmic membranes from suspensions of Staphylococcus aureus lysed by an enzyme recently isolated in these laboratories is described. These membranes contained: protein, 34.4%; ribonucleic acid, 6.6%; lipids, 34.5%; and total phosphorus, 1.4%. Such membranes exhibited adenosine 5'-triphosphatase (E.C. 3.6.1.3) activity, liberating orthophosphate at an initial rate of 0.53 mumole per min per mg of protein under optimal conditions. The enzyme was Mg(++)-dependent and K(+)- or Na(+)-stimulated. Maximal activity was observed with a molar adenosine 5'-triphosphate (ATP) to Mg(++) ratio of 1. One mole of orthophosphate was liberated per mole of ATP; the other product of digestion was adenosine 5'-diphosphate. Inorganic pyrophosphate and the 5'-triphosphates of guanosine, uridine, and cytidine were also attacked by membrane preparations, but more slowly than ATP. Ouabain, p-chloromercuribenzoate, and 2,4-dinitrophenol did not alter adenosine triphosphatase activity, whereas both Atebrine and chlorpromazine were inhibitory.

Adenosine triphosphatase activity of mycoplasma membranes

Rottem, Shlomo (Hebrew University, Jerusalem, Israel), and Shmuel Razin. Adenosine triphosphatase activity of mycoplasma membranes. J. Bacteriol. 92:714-722. 1966.-Adenosine triphosphatase activity of Mycoplasma laidlawii, M. gallisepticum, and Mycoplasma sp. strain 14 was confined to the cell membrane. The enzymatic activity was dependent on magnesium, but was not activated by sodium and potassium. Ouabain did not inhibit the adenosine triphosphatase activity of the mycoplasmas, and did not interfere with the active accumulation of potassium by M. laidlawii cells. Sulfhydryl-blocking reagents and fluoride inhibited the enzymatic activity, whereas 2,4-dinitrophenol was without any effect. Membranes of M. laidlawii hydrolyzed other nucleotide triphosphates and adenosine diphosphate (ADP), but at a lower rate than adenosine triphosphate (ATP). Nucleoside-2'-(3')-phosphates, ribose-5-phosphate, glucose-6-phosphate, and pyrophosphate were not hydrolyzed by the membrane preparations. It seems that the enzyme(s) involved in ATP hydrolysis by M. laidlawii membranes is strongly bound to the membrane subunits, which would account for the failure to purify the enzyme by protein fractionation techniques. The adenosine triphosphatase activity of mycoplasma membranes resembles in its properties that of similar enzymes studied in bacteria. The mycoplasma enzyme(s) seems to differ from the adenosine triphosphatase associated with ion transport in mammalian cell membranes and from mitochondrial adenosine triphosphatase.

The asparagine deamidase of Bacillus coagulans and Bacillus stearothermophilus

The purification and certain properties of L-asparagine deamidase of Bacillus coagulans and Bacillus stearothermophilus are described. Maximum enzyme activity was obtained at 55 °C. over a pH range of 7.5 to 8.5. The purified deamidase hyclrolyzed the L-isomer of asparagine quantitatively to aspartic acid and ammonia and did not attack the D-isomer. D-Asparagine inhibited the hydrolysis of the L-isomer. The Kmfor the inhibition reaction was found to be 1.87 × 10−2 M. The enzyme did not catalyze transamidation or hydroxylamine transfer reactions. Enzyme activity was inhibited by N-ethylmaleimide and p-chloromercuribenzoate. The inhibition by these agents was reversed by glutathione. In the absence of substrate the deamidase of both organisms was relatively heat labile at 55 °C. The heat lability of this enzyme is discussed in relation to the heat stability of other enzyme systems of thermophilic microorganisms.