Cellulolytic Enzymes During Morphogenesis in Dictyostelium discoideum

Abstract

Extracts from Dictyostelium discoideum at the sorocarp stage of development catalyzed the degradation of acid-swollen cellulose to d -glucose at an optimal p H of about 4.5; cellobiose and cellotriose were the major products from this degradation at p H 7.0. The optimal temperature at p H 7.0, when swollen cellulose was used as substrate, was about 45 to 48 C, and was somewhat lower at p H 4.2 to 4.5, i.e., about 40 C. To account for this degradation pattern, two types of enzymes have been characterized, cellulase(s) and β-glucosidase. With carboxymethyl cellulose as substrate, cellulase activity was not found in extracts prior to the sorocarp stage of development, but increased rapidly during aging of the sorocarp. Evidence is presented that at earlier stages of development the cellulase(s) is present in an inactive form. An inhibitor found in these extracts is heat-labile and probably of protein nature. The β-glucosidase is present at all stages of development and the specific activity changes about fourfold, the highest activity occurring during the culmination and sorocarp stages of development.