[Spontaneous solubilization of mcuosal peptide hydrolases in rat small intestine]. / Untersuchungen zur Spontansolubilisierung mucosaler Peptidhydrolasen des Dünndarms der Ratte.

In vitro incubations of small intestine preparation lead to the spontaneous release of mucosal enzymes into the incubation medium, due to superficial dissolution and membrane lesions. One-hour anaerobic incubation of everted small intestine segments produces the liberation of from 13% (leucine arylamidase) to 30% (Gly-L-Pro-splitting peptide hydrolase) of the mucosal enzyme activities. Under the conditions of in vivo perfusion, the solubilization rates are from 50 to 80% lower than these values. The tendency to solubilization is only in part reduced to a significant extent by the saturation of the incubation medium with oxygen, but it does not reach the in vivo level. The detectability of membrane-bound and intracellular marker enzymes in the incubation medium permits no conclusions concerning the physiological localization of the released peptidases.

Localization of hydrolysis and transport of dipeptides in the mucosa of the small intestine (established on the basis of the anoxic criterion).

The influence of anoxia on the hydrolysis and transport of certain dipeptides by the rat small intestine in vitro was investigated. It was shown that in most cases, during anoxia there is virtually complete inhibition of active transport, whereas the hydrolysis of dipeptides, both by the intact intestine and by homogenates of the mucosa, is unchanged. These data suggest an important role of membrane hydrolysis at the concluding stages of peptide digestion in the small intestine. The interrelationship of the two types of peptide hydrolysis: membrane and intracellular, is discussed on the basis of the data obtained.