Hormone evolution studies: multiplication promoting and imprinting ("memory") effects of various amino acids on Tetrahymena.

Aromatic, heterocyclic, polar and non-polar amino acids were examined for imprinting potential in a unicellular (Tetrahymena) model system. Serine gave rise to positive, glycine to negative imprinting, whereas valine, tryptophan, tyrosine and phenylalanine had no imprinting effect whatever. However, tyrosine and phenylalanine stimulated the division of Tetrahymena already at primary interaction, the former even for a relatively long time. It follows that amino acids, too, can give rise to imprinting, although their imprinting potentials are dissimilar. These phenomena have attracted attention to possible interrelationships between the supposed amino acid receptors of Tetrahymena and the evolution of amino acids to hormones.