LYSOSOMES AND INTRACELLULAR DIGESTION IN SEA STARS.

The study of lysosomes and intracellular digestion in sea stars seemed ideal. Echinoderms occupy an intermediate position in the phylogenetic progression from protozoan to mammal. A single sea star can cleanly provide a large amount of relatively homogenous pyloric caecal tissue, which is highly desirable for the biochemical determinations. Furthermore, the main pyloric caecal cells, namely, the columnar epithelial layer lining the lumen of the pyloric caecum, are assumed to be the major tissue involved in intracellular digestive activities. Investigations began with an histochemical examination of sea star tissues. Studies indicated the presence of granular particles of varying sizes with positive evidence for lysosomal enzymes. The project continued with the biochemical investigation of some of the lysosomal exzymes. After determining the optimal conditions for assays, sea stars were tested for these enzymes. The final phase of the study dealt with the isolation of the particles. In view of the high concentration of sucrose necessary to maintain the osmotic stability of the putative lysosomes, isolation by centrifugation proved to be diffucult. Preliminary data indicates that discontinuous gradient centrifugation may allow isolation of lysosomes in relatively pure form and relatively large amounts.