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

Abstract

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.

Lysosomal enzymes in extracellular digestion in the unicellular eukaryote Tetrahymena

“…The information given above permits the conclusion that phosphatases (Silberstein, 1979;Nielsen and Villadsen, 1985;Hunseler et al, 1987) present in the cell-free media from 24-h-old Tetrahymena cultures are sufficiently active in liberating phosphate from phosphorylcholine at pH 5.5 to initiate and support cell multiplication in a complete, but phosphate-free medium. The activity is reduced to 5-10% a t pH 7.5 as measured both with phosphorylcholine and p-nitrophenylphosphate as substrate (unpubl.…”

Μελέτη Του Ρόλου Των Φωσφοϊνοσιτιδίων Στο Μηχανισμό Της Φαγοκύτωσης

“…Το γεγονός ότι η έκκριση δε σχετίζεται με την παρουσία βλεννοκυστών ενισχύεται και από το ότι το μεταλλαγμένο στέλεχος T.thermophila MS-1, το οποίο δεν εκκρίνει λυσοσωμικά ένζυμα, εξωκυτώνει κανονικά ώριμες βλεννοκύστεις μετά από διέγερση των κυττάρων [Hünseler et al, 1987, Tiedtke et al, 1988, Leondaritis et al, 2005. Η υπόθεση ότι τα λυσοσωμικά ένζυμα προέρχονται από τον κυτοπρωκτό [Nillson, 1972, Nielsen et al, 1985 έχει επίσης απορριφθεί, αφού το μεταλλαγμένο στέλεχος T.thermophila ΝΡ1, το οποίο δεν σχηματίζει φαγοσώματα σε θερμοκρασία 37°C, έχει δείξει ότι εκκρίνει ένζυμα στο μέσο της καλλιέργειας [Silberstein, 1979]. Η έκκριση θα μπορούσε να γίνεται και από τους παρασωματικούς σάκους, παρόλο που αυτές οι δομές εμφανίζονται να έχουν λειτουργίες ενδοκύτωσης και όχι εξωκύτωσης [Nilsson et al, 1972].…”