The fresh milky latex extracted from 23 samples of Thai
C. papaya contained 40±13 mg protein and 529±162 units
protease activity/g wet latex. As papain is a protease of broad
specificity and no specific synthetic substrate is available, casein
was used as a substrate to determine the total protease activity
present in the latex while the purity of papain was determined
by electrophoresis and chromatography. On cathodic gel electrophoresis,
the proteins in the latex separated as five bands
(Fig. 1, lane 2). One of these proteins was identified as papain
according to its mobility that was equal to that of the standard
papain and its in situ proteolytic activity on polyacrylamide gel.
The electrophoretic analysis of the latex protein also indicated
that papain constituted about 8% of the total protease. This corresponds
to the earlier reports dealing with papain from different
sources of the latex [1,2,4]. The other components in the latex
were chitinase (∼22%) and three cysteine proteases including
chymopapain, glycyl endopeptidase and caricain,