Beta-1,3-glucanase from unfertilized eggs of the sea urchin Strongylocentrotus intermedius. Comparison with beta-1,3-glucanases of marine and terrestrial mollusks. beta-1,3-Glucanase (Lu) was isolated from unfertilized eggs of the sea urchin Strongylocentrotus intermedius. A comparative study of some properties of beta-1,3-glucanase Lu and beta-1,3-glucanases with different action types--endo-beta-1,3-glucanase from crystalline style of the marine mollusk Spisula sachalinensis (LIV) and exo-beta-1,3-glucanase from the terrestrial snail Eulota maakii (LII)--was performed. It was found that beta-1,3-glucanase Lu hydrolyzes laminaran with a high yield of glucose in the reaction products. The enzyme hydrolyzes substrates with retention of the glycosidic bond configuration, is able to cleave modified substrates, and exhibits transglycosylating activity. All properties of beta-1,3-glucanase from S. intermedius were more similar to those of the endo-beta-1,3-glucanase from the marine mollusk (LIV) than exo-beta-1,3-glucanase LII from the terrestrial snail. The differences in the effect of LIV and Lu on laminaran are probably related to the functions of beta-1,3-glucanase Lu from sea urchin eggs (which, in contrast to LIV, is not a digestive enzyme).