Based on substrate preferences, cercariae of Schistosoma
mansoni were seen
to express both cathepsin L and cathepsin B
cysteine proteinases, although the former activity was many
-fold greater.
Two
cathepsin L activities identified in cercarial
extracts by zymography co-migrated with activities in extracts of 3 h and
24 h
schisotosomula and in extracts of adult
worms. Since these enzymes have been implicated in haemoglob
in digestion
by
adult worms, they may perform a similar
function in schistosomula. Immunolocalization using scanning electron
micrographs showed that cathepsin L and
cathepsin B proteinases were present in the cercarial post-acetabular glands.
In addition, cercarial serine proteinase
activities considered to facilitate skin penetration efficiently cleaved
the
substrates Z-Gly-Pro-Arg-NHMec and Z-Gly-Pro-Lys-NHMec.
Cercariae release most of this serine proteinase activity when induced to
secrete the contents of their
acetabular glands. In contrast, newly transformed 3 h and 24 h schistosomula
did not express this activity.