Influence of duodenal secretions and its components on release and activities of human brush-border enzymes

The in vitro effects of human duodenal secretions and various combinations of its components on activity and release of enzymes from the human brush border were examined. Sucrase retained activity for 90 min in duodenal secretions, and maltase was almost as stable; lactase lost activity rapidly and alkaline phosphatase was of intermediate stability. Inactivation of lactase could only be partly (50%) attributed to luminal proteases, bile salts and phospholipids played no role. Rate of release of an enzyme from the brush border bore no relationship to its rate of inactivation. When individual proteases were studied, elastase was the most potent for releasing disaccharidases from the brush border; trypsin was ineffective alone but augmented the effect of elastase. Sucrase and maltase were activated by proteolytic release, but activation was abolished by simultaneous exposure of brush borders to bile salts. Lactase was released and rapidly inactivated by proteinases, while alkaline phosphatase appeared to be inactivated without significant release. These results show that there are significant interactions between luminal factors which have been inapparent when studying them in isolation. Loss of functionally useful enzyme does not follow release of sucrase or maltase from the brush border into the lumen but does follow release of lactase. Study of the susceptibility of lactase to inactivation by luminal factors in the various forms of lactose intolerance is warranted.     

Modulation of Aβ42 low-n oligomerization using a novel yeast reporter system

Background  

While traditional models of Alzheimer's disease focused on large fibrillar deposits of the Aβ₄₂ amyloid peptide in the brain, recent work suggests that the major pathogenic effects may be attributed to SDS-stable oligomers of Aβ₄₂. These Aβ₄₂ oligomers represent a rational target for therapeutic intervention, yet factors governing their assembly are poorly understood.     

Effects of Hydrostatic Pressure on Carcinogenic Properties of Epithelia

The relationship between chronic inflammation and cancer is well known. The inflammation increases the permeability of blood vessels and consequently elevates pressure in the interstitial tissues. However, there have been only a few reports on the effects of hydrostatic pressure on cultured cells, and the relationship between elevated hydrostatic pressure and cell properties related to malignant tumors is less well understood. Therefore, we investigated the effects of hydrostatic pressure on the cultured epithelial cells seeded on permeable filters. Surprisingly, hydrostatic pressure from basal to apical side induced epithelial stratification in Madin-Darby canine kidney (MDCK) I and Caco-2 cells, and cavities with microvilli and tight junctions around their surfaces were formed within the multi-layered epithelia. The hydrostatic pressure gradient also promoted cell proliferation, suppressed cell apoptosis, and increased transepithelial ion permeability. The inhibition of protein kinase A (PKA) promoted epithelial stratification by the hydrostatic pressure whereas the activation of PKA led to suppressed epithelial stratification. These results indicate the role of the hydrostatic pressure gradient in the regulation of various epithelial cell functions. The findings in this study may provide clues for the development of a novel strategy for the treatment of the carcinoma.     

Conflicting evidence regarding the transport of alpha-glutamyl-dipeptides by human erythrocytes.

A novel ninhydrin-positive compound, N-methyl-D-aspartic acid, was identified in the muscle extracts of the blood shell, Scapharca broughtonii. This compound is already known to have potent neuroexcitatory activity, inducing hypermotility and strong releasing action of serum luteinizing hormone in mammals. This may be, however, the first finding of N-methyl-D-aspartic acid in natural products.     

Stereospecificity and requirements for activity of the respiratory NADH dehydrogenase of Escherichia coli

The respiratory NADH dehydrogenase of Escherichia coli has been further amplified in vivo by genetic methods. The enzyme, a single polypeptide of Mr 47 200 of known amino acid sequence [Young, I. G., Rogers, B. L., Campbell, H. D., Jaworowski, A., & Shaw, D. C. (1981) Eur. J. Biochem. 116, 165-170], constitutes 10-15% of the total protein in the amplified membranes. In situ in the membrane, the enzyme contains 1 mol of FAD/mol of subunit and has a specific NADH:ubiquinone-1 oxidoreductase activity of approximately 1100-1200 units mg-1 at 30 degrees C, pH 7.5. The purified enzyme contains phospholipid, which remains closely associated with it during gel filtration on Sephacryl S-300 in the presence of 0.1% (w/v) cholate at low ionic strength. Under these conditions the enzyme is extensively aggregated (apparent Mr greater than 10(6]. This procedure yielded enzyme with a specific activity of 980 units mg-1, similar to the value observed in the membrane. This preparation contained less than 0.1 mol of Fe/mol of enzyme, confirming that Fe is not involved in reduction of ubiquinone 1 catalyzed by the enzyme. Neutron activation analysis of purified enzyme has demonstrated the absence of 35 trace elements including Se, Zn, Mn, Co, W, Cu, and Fe. The enzyme polypeptide, prepared completely free of phospholipid, FAD, and ubiquinone by gel filtration in the presence of sodium dodecyl sulfate, has been reactivated. The results show that the only components necessary for catalysis of ubiquinone-1 reduction by NADH in this system are the enzyme polypeptide, FAD, and phospholipid.(ABSTRACT TRUNCATED AT 250 WORDS)