FUNCTIONAL CHARACTERISTICS OF CALCIUM-SENSITIVE ADENYLYL CYCLASE
OF CILIATE TETRAHYMENA PYRIFORMIS
K. V. Derkach,1 A. O. Shpakov,1 Z. I. Uspenskaya,2 A. L. Yudin 2
1 Sechenov Institute of Evolutionary Physiology and Biochemistry RAS
and 2 Institute of Cytology RAS, St. Petersburg;
1 e-mail: alex_shpakov@list.ru
Calcium-sensitive forms of adenylyl cyclase (AC) were revealed in most vertebrates and invertebrates and
also in some unicellular organisms, in particular ciliates. We have shown for the first time that calcium cations
influence the AC activity of ciliate Tetrahymena pyriformis. These cations at the concentrations of 0.2—20 μM
stimulated the enzyme activity, and maximum of catalytic effect was observed at 2 μM Ca2+. Calcium cations at
a concentrations of 100 μM or higher inhibited the AC activity. Calmodulin antagonists W-5 and W-7 at the
concentrations of 20—100 μM inhibited the catalytic effect induced by 5 μM Ca2+ and blocked the effect at higher
concentrations of Ca2+. Chloropromazine, another calmodulin antagonist, reduced Ca2+-stimulated AC activity
only at the concentrations of 200—1000 μM. AC stimulating effects of serotonin, EGF and cAMP increased
in the presence of 5 μM Ca2+. AC stimulating effects of EGF, cAMP and insulin decreased in the presence of
100 μM Ca2+, and AC stimulating effect of cAMP decreased also in the presence of calmodulin antagonists
(1 μM). At the same time, stimulating effect of D-glucose in the presence of Ca2+ and calmodulin antagonists
did not change essentially. The data obtained speak in favor of the presence of calcium-sensitive forms of AC in
ciliate T. pyriformis which mediate enzyme stimulation by EGF, cAMP, insulin, and serotonin.
Key words: adenylyl cyclase, calmodulin antagonist, ciliate, calcium, serotonin, cyclic adenosine monophosphate,
epidermal growth factor, Tetrahymena pyriformis
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