Pleiotropic Effects of a Temperature‐Sensitive Mouthless Mutation in Tetrahymena thermophila on the Excretion of Extracellular Enzymes

The mode of enzyme excretion was investigated during balanced growth in wild type Tetrahymena thermophila and in a temperature‐sensitive mutant that did not form a mouth and food vacuoles at the restrictive temperature. The mutant was used to determine which of the extracellular enzymes are normally excreted by defecation. During balanced growth at the permissive temperature the excretion of enzymes was constant, and maximal in complex medium. No protease activity against azocasein was detected. Changes in the growth temperature of the wild type cells only affected the release of 3′‐nucleotidase. For the mutant, however, the excretion changed markedly with increasing temperature: (a) ribonuclease, deoxyribonuclease, α‐glucosidase, and β‐glucosidase were detected in 0–10% of normal amounts; (b) 3′‐ and 5′‐nucleotidase, not measured previously in Tetrahymena , were found in 10‐ to 14‐fold of normal amounts; (c) excretion of acid phosphatase was unaffected. We therefore conclude that the extracellular enzymes (a) are released by defecation, that 3′‐ and 5′‐nucleotidase are secreted through the membrane system, and that acid phosphatase is released by lysosomes emptied through pinocytosis. It is proposed that the lysosomes used for the formation of digestive vacuoles are different from those used for the formation of pinocytotic vacuoles and for autophagic vacuoles.