Fractionation of an Esterase from Calf Spleen Implicated in the Detoxification of Bacterial Endotoxin ∗

Discussion and Summary

The use of the two successive fractionation procedures resulted in the preparation of an esterase-rich fraction which was capable of detoxifying endotoxin. The partial inhibition of esterase activity—but not detoxifying power—by DFP or TEPP indicated that the final Sephadex Fraction II contained a cholinesterase-type enzyme not involved in the detoxification reaction. The concentration of DFP employed was sufficient to have inhibited the esterolytic activity of proteases such as trypsin or chymotrypsin, if present. Consequently, the bulk of the enzyme in Fraction II which was active in the detoxification of endotoxin is considered for the present to be an esterase of the nonspecific, carboxylic type. Most of the esterase activity present in DEAE-cellulose Fractions I and III (Fig. 1) was inhibited by DFP and these fractions possessed only a weak capacity to inactivate endotoxin.

Whereas the spleen enzyme is considered to be a nonspecific esterase of the type found in normal serum, it differs from the latter in some important respects. The degradation and inactivation of endotoxin in serum or plasma was reported to occur as a two step reaction requiring two different esterases, one of which was a lipoprotein esterase (4). Although not yet established, it appears that in the spleen fraction only one esterase functions in the degradation and inactivation of endotoxin. The spleen esterase is not associated with a lipoprotein and no lipoprotein was detected in the isolated fraction. The spleen esterase also differs from the plasma esterases in chromatographic behavior and in heat stability.