THE ISOLATION AND CHARACTERIZATION OF SUBCELLULAR COMPONENTS OF THE EPITHELIAL CELLS OF RABBIT SMALL INTESTINE

1. Homogenization of the epithelial cells of rabbit small intestine in 0.3m-sucrose-5mm-EDTA, pH7.4, maintains intact the microvillus sheets that form the lumenal surface of the cells, the nuclei, the mitochondria and the vesicles (microsomes) formed from the endoplasmic reticulum. 2. These particulate components of the cell, and the cell-sap fraction, have been isolated by differential centrifuging of cell homogenates. 3. The nuclei and microvillus sheets sediment together and it has been impossible to separate these subcellular components by centrifugal methods. 4. The isolated subcellular fractions have been identified by a combination of light-microscopic examination, electron-microscopic examination, chemical analysis and assay for selected enzyme activities.

THE REDUCTION OF INORGANIC SULPHATE TO INORGANIC SULPHITE IN THE SMALL INTESTINE OF THE RAT

1. Whole scrapings of rat intestinal mucosa were incubated with carrier-free sodium [(35)S]sulphate. Radioactivity was found in S-sulphocysteine and to a small extent in S-sulphoglutathione. 2. Whole scrapings of rat intestinal mucosa incubated with carrier-free sodium [(35)S]sulphate and oxidized glutathione formed S[(35)S]-sulphoglutathione as the main radioactive product. The amount of S[(35)S]-sulphocysteine formed was considerably lower than in a control that contained no oxidized glutathione. 3. The supernatant fraction of homogenates of rat intestinal mucosa catalyses the NADPH-dependent reduction of adenosine 3'-phosphate 5'-sulphatophosphate to inorganic sulphite. NADH or GSH fail to replace NADPH as reducing agents. 4. The formation of inorganic [(35)S]sulphite from inorganic [(35)S]-sulphate may account for the incorporation of [(35)S]sulphate into S-sulphoglutathione by the small intestine of the rat in vivo and in vitro.

ABORTIVE INTESTINAL INFECTION WITH AN ESCHERICHIA COLI-SHIGELLA FLEXNERI HYBRID STRAIN

Formal, Samuel B., (Walter Reed Army Institute of Research, Washington, D.C.), E. H. LaBrec, T. H. Kent, and S. Falkow. Abortive intestinal infection with an Escherichia coli-Shigella flexneri hybrid strain. J. Bacteriol. 89:1374-1382. 1965.-The mechanism of the apparent loss of virulence of an Escherichia coli-Shigella flexneri hybrid strain was studied. The parent Shigella strain caused a fatal enteric infection when fed to starved guinea pigs, and signs of dysentery followed its oral administration to monkeys. The hybrid strain failed to produce any apparent symptoms when fed to either of these species. The parent strain was shown to invade the intestinal mucosa of starved guinea pigs. This caused a severe inflammatory reaction in the lamina propria, which progressed to ulceration of the intestinal epithelium and resulted in death of the animal. The hybrid strain also invaded the intestinal mucosa and produced an inflammatory reaction. In this case, the inflammatory reaction subsided, the intestine returned to normal within 4 days after challenge, and the animal survived. Both fluorescent-antibody techniques and in vivo growth studies have shown that the hybrid strain can not maintain itself in the intestinal mucosa. Preliminary studies have indicated that a similar situation also exists in the monkey. It is concluded that the virulence of dysentery bacilli rests not only in the capacity to reach the lamina propria, but also in the ability to multiply in this region.

THE METAL ION ACTIVATION OF THE ALKALINE BETA-GLYCEROPHOSPHATASE OF RABBIT SMALL INTESTINE

1. A fraction of intestinal epithelial cells from rabbit small intestine that contained nuclei and microvillus membranes served as a source of alkaline-beta-glycerophosphatase activity. 2. The greater part of the enzyme activity could be released from the subcellular particles by disintegration of the latter, followed by centrifugation at 40000g and butanol extraction of the resulting sediment. 3. Further purification of the enzyme was achieved by diethylaminoethylcellulose chromatography and by gel filtration. 4. Dialysis of the purified enzyme preparations against EDTA gave an essentially inactive enzyme. High activity could be restored by adding Zn(2+)+Mg(2+), Zn(2+)+Co(2+), Mg(2+)+Co(2+) or Co(2+) alone to these inactive preparations. Neither Zn(2+) nor Mg(2+) added singly to the assay system restored more than a small part of the enzyme activity. 5. The optimum Zn(2+) concentration was about 0.2-1m-equiv./l., whereas Mg(2+) and Co(2+) had optimum concentrations about 30-60m-equiv./l. 6. If added in excess of the optimum concentration, Zn(2+) strongly inhibited the enzyme under all conditions tested. 7. In the presence of an optimum concentration of Co(2+) (33m-equiv./l.) in tris buffer at the optimum pH (8.8 at 37 degrees ), K(m) for the beta-glycerophosphatase was 0.3mm.

BIOSYNTHESIS OF VITAMIN A WITH RAT INTESTINAL ENZYMES

Vitamin A is synthesized from beta-carotene in cell-free homogenates of rat intestinal mucosa, the biosynthetic enzymatic activity being present in the soluble protein fraction of the homogenate. Also required are a heat-stable factor in the particulate fraction, molecular oxygen, and bile salts. The reaction is stimulated by glutathione. The product, obtained in yields of up to 50 percent, has been identified as vitamin A aldehyde (retinal) by way of its semicarbazone derivative. The reaction mechanism involves the central cleavage of beta-carotene into two molecules of retinal.