Sera from mice infected with Schistosoma mansoni were found to contain substantial amounts of an acid-active hemoglobinolytic enzyme. Recovery of this enzyme from aliquots of pooled 12-week infected serum, using a phenylalanine-agarose affinity column, showed that a portion of the enzyme binds tightly to the column at pH 4.0, and can be eluted with 0.01 M formic acid. Another larger portion of hemoglobin-digesting activity is not bound to the column and emerges with the buffer front. Sera from rats which were exposed to cercariae, but in whom worms were stunted and did not develop to maturity, were found not to contain hemoglobin-active protease. At the present time, the source of the enzyme has not been unequivocably proven. The enzyme found in the serum binds to and releases from the affinity column in the same manner as does hemoglobinase recovered from freeze-dried S. mansoni worms. Maximal activity of both enzymes against the substrate occurs at pH 4.5–5.0. Present evidence suggests that the protease present in the serum is of worm origin. It is postulated that this protein may be excreted by the parasite during the process of regurgitation of gut contents. Presence of worm enzyme circulating in the host plasma would correlate with the known sensitization of the host to schistosomal hemoglobin-digesting enzyme.
Visiting Scientist, Tel Aviv University Medical School, Tel Aviv, Israel.