FACTORS EFFECTING THE THERMOSTABILITY OF CYSTEINE PROTEINASES FROM CARICA-PAPAYA

Thermal denaturation of four Carica papaya cysteine proteinases (papai n, chymopapain, papaya proteinases 3 and 4) was studied as a function of pH using high-sensitivity differential scanning calorimetry. The ra tios of calorimetric enthalpy to Van't Hoff enthalpy suggest that, for all these proteins, denaturation occurs as a non two state process, v ia an intermediate structure. Differences in the thermal stabilities o f the proteinases; chymopapain > papaya proteinase 3 > papain > papaya proteinase 4, were correlated to their amino acid sequence to explain the observations in terms of mobility and specific residue mutation. Three-dimensional structures of papain and papaya proteinase 3 were si milarly used to illustrate the influence of atomic mobility on stabili ty.