The Structure of Papain

Abstract

Publisher Summary The fruits of the tropical papaya tree have latex that contains several enzymes. This chapter focuses on two different proteolytic enzymes: chymopapain and papain. Both enzymes belong to the group of proteolytic plant enzymes that require a sulfhydryl group for activity. The chapter discusses the enzymatic properties of papain. Papain can catalyze a number of reaction—namely, acyl-enzyme intermediate, hydrolysis, transferase action, and specificity. X-ray diffraction can provide a wealth of information on a protein structure. The papain molecule consists of one folded polypeptide chain of 212 residues. The sequence determination of these residues is an example of the mutual interaction between purely chemical and X-ray methods. Because of the many difficulties that papain presented to the chemists, only a tentative sequence could be published in 1964. Some of the overlaps were not found to be as conclusive as desired, and at least one gap existed in the sequence. The available information, however, permitted the interpretation of the electron density map. Moreover, the difficulties in the early chemical sequence studies on papain because of the insolubility of the denatured protein and many of its peptides is circumvented by the use of completely carboxymethylated papain that has been fully maleylated.