The galactan-degrading enzymes in the snail Biomphalaria glabrata.

1. Embryonic snails incorporate from the perivitelline fluid in which they are embedded a polysaccharide, called galactan, which is composed entirely of D-, or D- and L-galactose. In this investigation the p-nitrophenyl-beta-D-galactoside degrading enzyme of Biomphalaria glabrata which was assumed to be involved in the degradation of the galactans was purified almost to homogeneity and its specificity was studied. 2. It has a mol. wt of 135,000 and is composed of two identical subunits. 3. It could be shown that p-nitrophenyl-beta-D-fucoside was hydrolysed eight times faster, but native galactan was neither decomposed nor was it inhibitory for the hydrolysis of p-nitrophenyl-glycosides. 4. Thus, it is most likely that this galactosidase is not involved in the galactan metabolism. 5. However, a membrane-bound enzyme complex was revealed which was able to metabolize the native galactan of Biomphalaria glabrata completely and which showed graded reactivity towards galactans of other species. 6. Since no intermediate degradation products were found it must be assumed that they were metabolized further in the mitochondria.