Localization of peptide hydrolysis in the enterocyte and the transport mechanisms of apical membrane.

1. The absence of the effect of anoxia on the hydrolysis rate of a number of dipeptides and one tripeptide by the intact and homogenized mucosa of the small intestine in different mammals (rat, mouse and guinea pig) has been demonstrated. 2. It has been shown that in rats anoxia inhibits intestinal transport both of free glycine and glycine formed during the hydrolysis of Gly-Leu, Leu-Gly, Gly-Pro but not Pro-Gly. 3. Data obtained using the anoxic criterion suggest that the systems of membrane hydrolysis of peptides with the subsequent absorption of released amino acids presents a dominant mechanism of protein assimilation under normal physiological conditions. 4. However, they do not exclude the possibility of the transport of peptides across the apical membrane of enterocytes.

[Mechanisms of the protective action of cryoprotectors on Escherichia coli cells]. / O mekhanizmakh zashchitnogo deistviia krioprotektorov na kletki Escherichia coli.

Two classes of cryoprotectors, namely, glycerol (penetrating the cell) and dextran with a mol. mass of 15-20,000 Da (non-penetrating the cell), were tested for their ability to exert a protective effect on the permeability and viability of Escherichia coli M 17 cells subjected to different freezing conditions. Cell permeability assayed in terms of the release of low-molecular-weight compounds into the surrounding medium was shown to be disordered to a far less extent when dextran was used as a cryoprotective agent than in the case of glycerol. The cells were found to be resistant to lysis stimulated by the detergent sodium lauryl sulfate (0.02%) in the presence of dextran. The cells were still capable of forming colonies after their freezing to -10 degrees C in the presence of the cryoprotectors in media containing the detergent (2%). Once the cells had been frozen to -196 degrees C, only those protected by glycerol were resistant to the detergent in the growth medium. Different mechanisms of the cryoprotective action on E. coli cells are discussed.

[Effect of inhibitors on the viability and protein and nucleic acid synthesis of Escherichia coli]. / Vliianie nekotorykh ingibitorov na zhiznesposobnost', sintez belka i nukleinovykh kislot u Escherichia coli.

The object of this work was to study how the synthesis of protein, RNA and DNA in Escherichia coli M17 and its viability were influenced by chloramphenicol (50 and 300 micrograms/ml) an inhibitor of protein biosynthesis, and sodium azide (200 and 2000 microM) and aminazine (50 micrograms/ml), inhibitors of respiration. The exposed were inhibitors with the bacteria for 60 min at room temperature and for 1-4 months at -10 degrees C. The inhibition of the E. coli viability by chloramphenicol was shown to be reversible. The respiration inhibitors stabilized its viability upon storage at -10 degrees C for one month. The inhibitors were found to produce a different effect on the synthesis of RNA and protein in E. coli. The rates of DNA synthesis hardly changed. No correlation was established between changes in the synthesis of protein and nucleic acids by E. coli after the action of the inhibitors and its viability.

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.

Membrane and intracellular hydrolysis of peptides: differentiation, role and interrelations with transport.

The possible relative importance of the membrane and intracellular peptidases of the enterocytes in splitting dietary peptides to amino acids has been analysed. On the anoxic criterion, membrane hydrolysis was found to be predominant. Model experiments revealed cooperative interactions between the membrane enzyme and the coupled transport system. This cooperativity allows the main characteristics of oligomer transport to be described in terms of membrane digestion. Comparison of the behaviour of membrane and intracellular peptidase under different conditions has shown that the former are largely involved in digestion and the latter in intracellular metabolism. It is suggested that the efficiency of the membrane system is high enough to account for the hydrolysis of protein, especially taking into account the stimulation of enzyme processes in the brush border that occurs after ingestion of protein and carbohydrate. A sequential model based on the concept of three interacting enzyme layers (glycocalyx, lipoprotein membrane and cytosol) is presented.