Evidence for Lysosomal Enzymes in Acanthamoeba and Their Activity Changes During Encystment

Abstract

Assays on cell-free homogenates of Acanthamoeba castellanii reveal that the three hydrolases, acid phosphatase (APase), acid deoxyribonuclease, and acid ribonuclease (RNase), possess pH optima of 5.0, 4.8, and 5.2, respectively. These enzymes exhibit an enhanced sedimentation at 20,000 x g when sucrose is in the homogenizing buffer. Treatment of homogenates with Triton X-100 increases total enzyme activity. These results suggest that the enzymes are particle-bound in lysosomes. During encystment there is a differential decrease in the activity per cell of all three enzymes, with RNase decreasing most rapidly and APase least rapidly. The specific activity of APase increases during encystment even though its activity per cell gradually decreases.