Characterization of an adenylyl cyclase activity in particulate preparations from epimastigote forms of Trypanosoma cruzi.
Particulate preparations from epimastigote forms of Trypanosoma cruzi contain an adenylyl cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) which could be stored at --20 degree C and resisted 5 cycles of freezing and thawing over 10 days without significant loss of activity. The enzyme reaction strictly required Mn2+, had a pH optimum of 7.7 and was not inhibited or stimulated by NaF. Particles prepared in the presence of 10 mM Mn2+ or Mg2+ were 3--4 times more active than particles prepared in the absence of these cations. However, Mg2+ could not substitute for Mn2+ during enzyme assay nor did it enhance activity in the presence of saturating concentrations of Mn2+. The binary complex Mn - ATP2- was shown to be the true substrate for the adenylyl cyclase and free ATP was highly inhibitory. Plots of enzyme activity against equimolar concentrations of ATP - Mn gave sigmoid curves with n values in Hill plots ranging between 1.5 and 2.0. Excess Mn2+ activated the cyclase catalyzed reaction at low but not at high concentrations of ATP - Mn. In the presence of an excess of 1 mM Mn2+, which transforms 97% of the added ATP to productive Mn - ATP2- complex, the substrate saturation curve assumed a Michaelian pattern with an apparent Km =0.2 mM.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002413:Cations, Divalent; D004789:Enzyme Activation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D014349:Trypanosoma cruzi / Q000201:enzymology*
D002413:Cations, Divalent; D008345:Manganese; D000255:Adenosine Triphosphate; D000262:Adenylyl Cyclases; D008274:Magnesium