A STUDY OF ENZYMATIC DEGRADATION OF A MACROMOLECULAR SUBSTRATE, POLY[N-5-(2-HYDROXYETHYL)-L-GLUTAMINE], BY GEL-PERMEATION CHROMATOGRAPHY AND KINETIC MODELING

The enzymatic degradation of poly[N-5-(2-hydroxyethyl)-L-glutamine] (P HEG) by papain was investigated with the aim of evaluating the role of the random and/or a non-random mechanism of cleavage. The random degr adation was modelled experimentally by the reaction of PHEG with ethan olamine. Assuming that different mechanisms of cleavage would yield di fferent molecular weight distributions (MWDs) of the polymer degraded to the same degree, the evaluation was based on the comparison of expe rimental MWDs, measured by gel permeation chromatography, with MWDs si mulated kinetically for the assumed mechanism of degradation. While a very good fit through a broad range of degradation conversions was obt ained between the MWDs simulated for a random process and the experime ntal MWDs of the degradation of PHEG by ethanolamine, the enzymic degr adation of PHEG by papain was certainly not a random process. Two mode ls were found to be compatible with the chromatographic data: (i) a mu ltiple attack assuming that the subsequent cleavage may proceed only o n one of the two fragments produced by the previous attack, or (ii) a model which assumes that the degradation rate of one bond in a macromo lecule of molecular weight M is proportional to M(-1/3), i.e. a model which stresses the role of the surface of the polymer coil. In both si mulations of enzymic degradation, the two bonds on each end of the PHE G chain were assumed not to be cleavable.