Turnover and intranuclear localization of 125I-insulin in Tetrahymena. An autoradiographic study

The unicellular Tetrahymena first internalized, then partly released the labelled insulin. Insulin-pretreated (imprinted) Tetrahymena cells behaved differently from non-pretreated cells, in that they retained a greater part of internalized insulin in the cytoplasm. Additional exposure to excessive non-labelled (cold) insulin caused a decrease in intracellular labelled insulin retention. Internalized insulin also entered the nucleus of Tetrahymena, where it was found in a heterochromatic localization.