THE STUDY OF MOLECULAR MECHANISMS OF ACTION OF NATURAL AMINO ACIDS AND SEROTONIN ON ADENYLYL AND GUANYLYL CYCLASES OF THE CILIATES
It has been previously shown that some amino acids and their derivatives are capable of regulating the activity of adenylyl cyclase (AC) and guanylate cyclase (GC) in free-living ciliates <i>Dileptus anser </i>and <i>Tetrahymena</i>. The aim of this work was to study the molecular mechanisms of action of methionine, tyrosine, alanine and neurohormone serotonin on the activity of enzymes-cyclases and the identification of their specific receptors in <i>D. anser </i>and <i>T. pyriformis</i>. Methionine and serotonin significantly increased the basal AC activity in both ciliates, and the AC effect of serotonin in <i>T. pyriformis </i>was carried out with the participation of Ca2+-dependent form of AC and heterotrimetic G proteins. AC stimulating effect of tyrosine and alanine was expressed weakly and only detected in <i>D. anser</i>. Serotonin is both ciliates and alanine in <i>D. anser </i>stimulated GC activity, whereas methionine and tyrosine had no effect on GC. Methionine and serotonin bind to surface receptors of the ciliates with high affinity. KD for [methyl-3H] methionine binding to <i>D. anser </i>and <i>T. pyriformis </i>were 7.5 and 35.6 nM, and for [3H] serotonin binding were 2.7 and 4.7 nM, respectively. Alanine and tyrosine bind to the ciliates with low affinity. Thus, ciliates <i>D. anser </i>and <i>T. pyriformis </i>have chemosignaling systems regulated by amino acids and their derivatives and including the enzymes with cyclase activity. There is an assumption that these systems are similar to hormonal signaling systems of higher eukaryotes and are their predecessors.