Developmental expression of cathepsin D aspartic protease in Schistosoma japonicum

Schistosomes utilise haemoglobin from ingested host erythrocytes as their m ain source of amino acids. Using reverse-transcriptase PCR, we detected tra nscripts encoding cathepsin D in eggs, miracidia, and adult male, female an d mixed-sex Schistosoma japonicum. Using the synthetic fluorogenic peptide, o-aminobenzoyl-isoleucyl-glutamylphenylalanyl-p-nitro-phenylalanyl-arginyl -leucine-NH2, and human haemoglobin as substrates, we detected cathepsin D- like aspartic protease activity at pH 3.6 in extracts of these developmenta l stages which was completely inhibited by the addition of 10 mu M pepstati n, Using immunoblotting with rabbit antibodies raised against recombinant S . japonicum cathepsin D, we detected the aspartic protease in extracts of a ll developmental stages examined, although it appeared to be expressed at h igher levels in the adult female schistosome. These results indicate that ( almost) all stages of S. japonicum express an aspartic protease. Moreover, they are consistent with the hypothesis that this enzyme plays a key role i n maturing and adult schistosomes in the proteolysis of host haemoglobin fr om ingested erythrocytes. (C) 1999 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.