Studies on polygalacturonase of certain yeasts

Abstract

1. 1. Among a considerable number of yeast species, representing nearly all yeast genera, only six were found which were capable of causing certain changes in pectin, when grown in its presence. These six cultures could all be identified with Saccharomyces fragilis (and a variety of this species) and its imperfect form Candida pseudotropicalis, as well as certain varieties of the latter. (See Discussion section.) These organisms cannot use pectin as a source of carbon, but require an added sugar for development. 2. 2. S. fragilis var. No. 351 was used for most of the studies reported herein. When it was grown in the presence of pectin, clarification of the liquid culture media took place with the formation of an amorphous precipitate consisting of about 1% of the pectin added. The jellying power of the pectin is destroyed, but the amount of calcium pectate and alcohol precipitate, obtainable from a clarified solution, is practically unchanged as compared to control solutions. 3. 3. The action was found to be due to an exocellular, nonadaptive, polygalacturonase-like enzyme, free of pectinesterase. The action of this yeast polygalacturonase is characteristic in that pectic acid, when used as a substrate, is only partially hydrolyzed. In contrast to fungus polygalacturonase, the enzyme cannot hydrolyze pectic acid completely to monogalacturonic acid. The velocity constant of the (initially) first-order reaction was found to be 0.196 at 22 °C. and at a pH of 3.40. The optimum pH was approximately 3.5–4.0, and the maximum rate was in the region of 55–60 °C.