Chemotactic-range-fitting of amino acids and its correlations to physicochemical parameters in Tetrahymena pyriformis--evolutionary consequences.

Amino acids are considered the oldest organic substances of the prebiotic evolution. Chemotactic effects of amino acid L-isomers investigated in the protozoan model Tetrahymena show that the chemotactic properties of amino acids are complex and depend on multiple physicochemical characteristics of the investigated ligands. The range of effectiveness is significantly wider for chemoattractant ligands than for chemorepellent ones. This phenomenon provides the basis of the "chemotactic-range-fitting" theory. The validity of this theory is supported by a decreased pK (-COOH), an increased pK (-NH2), and a decrease in solvent exposed areas and hydropathy indexes in chemoattractant amino acids compared to chemorepellent ones. Chemotactic selection has proven the activity of long-term (I, H, T) and short-term (P, A, Q, S) selector amino acids and their characteristic diversities in values of the pK and SEA (surface exposed area). Comprehensive studies of the chemotaxis data with the results of consensus analysis of amino acids suggests that chemotactic activity was one of the most primordial physiological activities and had a prospective significance not only in the molecular evolution of ligands, but also in the evolution of signalling.