The application of a new affinity ligand to the fractionation
of cysteine proteinases from papaya latex led
to the discovery of an enzyme named papaya proteinase
IV [ 11. This has a substrate specificity very different
from the other known papaya cysteine proteinases, and
is not inhibited by chicken cystatin [l]. We now report
the complete amino acid sequence of the enzyme, showing
that it is a member of the papain superfamily of
proteins, but with some unusual amino acid substitutions.