Papain is an enzyme. It is a cysteine peptidase that is found in papaya. It uses a cysteine amino acid to cleave other polypeptide bonds. It has been commonly used as a meat tenderizer.
As an enzyme, papain consists of a long polypeptide chain composed of many amino acids. Its molecular weight is over 23,000 daltons. As such it is a solid and will not have a defined boiling point. It is designed to work at an optimum temperature of about 65 degrees C. If heated too hot, papain will start to denature, or break down, instead of boil cleanly. A more useful physical property here would be the melting point, but I cannot seem to find one (which might mean that it doesn't melt cleanly either). As a final point, you cannot heat any boiling liquid higher than its boiling point.