Human milk lipase substrates: electronic role.

The hydrolysis of a series of 4'-nitrophenyl 4-substituted benzoates, catalyzed by human milk lipase in the absence and presence of cholate stimulation, has been measured at pH 7.3, 37.5 degrees C. There is no evidence for an acyl site electronic interaction in the rate determining step of the esterolytic reaction. Substrate inhibition, arising from restricted rotation of the aryl residues about the ester linkage in the esterolytic site, is exhibited by these substrates.