THE NATURE OF NONSPECIFIC ESTERASES A SUBUNIT CONCEPT

To investigate the nature of esterase polymorphism, nonspecific esterases were investigated in a large number of organs obtained from rat. In starch gel electropherograms the capacity of ester hydrolysis was seen to decline predictably with successively longer chain carbon substrates. An increasing susceptibility to organophosphate inhibition was observed with progressive lengthening of the acyl chain in the substrate molecules. Attempts to hybridize an organophosphate-sensitive esterase with a resistant type yielded a few additional esterase species. Studies on an esterase fraction isolated by column chromatography revealed the highly relative nature of organophosphate inhibition. These suggested that nonspecific esterases all belong to one enzyme system that does not justify the present compartmentation into acetyl-, aryl- or carboxylesterases on grounds of substrate hydrolysis or organophosphate sensitivity. It is likely that esterase species are each built on a subunit structure and exhibit overlapping specificities through sharing of common subunits. The concept that a whole range of esterase subunits exist, each varying in its capacity to hydrolyze esters of up to an optimal chain length and arranged according to the dictates of specific tissue requirements, is in accord with the present findings.