Biochemistry international最新文献

Amyloid beta-protein, the major constituent of amyloid plaques in Alzheimer's disease, is derived from larger amyloid precursor proteins (APP). Changes in the rates and or pathways of APP synthesis and degradation may be central to the deposition of beta-amyloid. We explored the possibility that APP processing is regulated by activation of endogenous cell-surface neurotransmitter receptors by stimulating C6, PC12 and neuroblastoma cells with the cholinergic agonist carbachol. We measured the intracellular APP in these cell lines by western blotting using three antibodies against different regions of APP. When cells were treated with carbachol for different periods, PC12 and C6 cells responded with a sharp decrease of APP bands. Similar blots probed with an antibody against heat-shock protein (HSP), showed no change in the intensity of the immunoreactive HSP-70 band. These results suggest that the decrease in intracellular APP seen after stimulation by carbachol has some specificity and that APP processing may be regulated by stimulation of cholinergic receptors on the surface of cells.

Gossypol, a polyphenolic binaphthyl dialdehyde found in cotton seeds, is a dietary mutagen and a potential male contraceptive. We have earlier shown that in the presence of Cu(II) gossypol causes strand breakage in double stranded DNA and that active oxygen species are involved in this reaction. In this paper we present experiments to suggest that gossypol may be oxidised by Cu(II) to a gossypol radical that may directly react with DNA. Changes in absorption spectrum and fluorescence emission spectrum of gossypol indicated that it binds to both double stranded and single stranded DNA. Gossypol and Cu(II) were shown to form a charge transfer complex that decayed in an oxygen independent reaction. The rate of DNA degradation by gossypol-Cu(II) complex was found to be the same both in the presence and absence of molecular oxygen.

Saccharomyces cerevisiae, Schizosaccharomyces pombe, Endomyces magnussi, Lodderomyces elongisporus and Rhodotorula gracilis, yeast species ranging from a glycolytic type to a strictly aerobic one, were tested for the activity of their plasma membrane H(+)-ATPase and the effect of alkaline metal cations thereon. The ATP-hydrolyzing activity of membranes from glucose-activated cells ranged from 456 to 932 mumol inorganic phosphate released per min per 1 g membrane protein. The effect of 0.2 M Li+, Na+, K+, Rb+ and Cs+ never exceeded the statistical range of error. In contrast, acidification after glucose addition ranged from 0.15 (for R. gracilis) to 14.8 nmol H+ per min per mg dry weight (for S. cerevisiae) and it was markedly influenced by the presence of alkaline metal chlorides, the highest effect observed being a seven-fold increase by K+ in a S. cerevisiae suspension. The effects were additive to those observed without ions in solution and are ascribed to the operation of independent channels and/or exchange systems for H+ with a clear selectivity toward K+. The separate nature of the ion-triggered extracellular acidification is supported by a different ratio of titration to pH-derived acidity with and without K+.

The intragastric administration of alcohol to pregnant mice at 3.0 g/kg body weight, but not at 0.5 or 1.5 g/kg body weight, adversely influenced embryonic growth and increased the rate of methyl group incorporation from S-adenosyl-L-[methyl-3H]methionine into uterine endometrial plasma membrane phospholipids. These changes involved phosphatidylcholine, phosphatidyldimethylethanolamine, and phosphatidylmonomethylethanolamine when the alcohol was acutely administered, but only phosphatidylcholine when the drug was given in a semi-chronic regime. Similar alterations were not detected in post-implantation embryos exposed to alcohol either in vitro or in vivo. The results suggest that maternal exposure to alcohol during early post-implantation pregnancy can alter the pattern of phospholipid methylation in the uterus, but not in the embryo, which may facilitate biochemical changes that adversely influence the ability of the maternal system to support embryonic development.

The activity of acid alpha-mannosidase in phenotypically characterized lymphoid cells, isolated from peripheral blood, spleen and lymph nodes of patients with various lymphoproliferative disorders has been studied. Cells with different immunophenotypes were shown to have different alpha-mannosidase activity levels. The lowest alpha-mannosidase activity was observed in cells phenotypically corresponding to early B cells obtained from B-CLL patients. The highest activity was determined in cells with phenotypes of activated, CD11c-expressing B cells from B-NHL and HCL patients. There were considerable differences in alpha-mannosidase activity between peripheral blood and spleen lymphoid cells of B-NHL patients with spleen damage. The data obtained may be used in classification, primary diagnosis and staging of hematopoietic malignancies.

The purpose of the present study was to purify and kinetically characterize N-acetyl-beta-D-hexosaminidases A and B (EC 3.2.1.52) from the caput, corpus and caudal regions of the adult rat epididymis. The molecular mass of the purified native enzyme was approximately 250,000 and approximately 223,000 daltons for the A and B isozymes, with a subunit molecular mass of approximately 63,000 and approximately 56,000 daltons, as determined by size exclusion chromatography and gel electrophoresis under reducing conditions. The apparent Michaelis-Menten constant and maximum velocity values were 0.60, 1.55 and 0.68 mM and 0.54, 3.20 and 2.30 microM/min./mg protein for the enzyme purified from the caput, corpus and caudal regions, respectively. These values were determined by using p-nitrophenyl-N-acetyl-beta-D-glucosaminide as the substrate. These data suggest that the enzyme may be more active in the corpus region of the epididymis than in the caput and caudal regions.

Application of heparin, polyadenylate, polyglutamate and polygalacturonate resulted in changes in the electron absorption spectrum of cytochrome c that resembled those after cytochrome c oxidase application at neutral pH. The formed complexes of cytochrome c with polyanions retain the bond of Met-80 with heme iron. Cytochrome c oxidase and the polyanions increased the apparent pKa of alkaline transition of cytochrome c by an order of magnitude.

The non-nuclear membranes and the nuclei prepared from L1210 cells catalyze the in vitro transfer of N-acetyl(14C)glucosamine from UDP-N-acetyl(14C)glucosamine to endogenous glycoprotein acceptors. Adequate analysis of these acceptors have demonstrated that the nucleus has its own N-acetylglucosaminyltransferase system that leads to the formation of N-N'-diacetylchitobiosylated proteins.

A protease activity directed toward high molecular weight salivary mucus glycoprotein was identified in the secretion of human submandibular salivary gland. The protease exhibited maximum activity at pH 7.0-7.4, and following ammonium sulfate fractionation yielded an active enzyme at 60% saturation which on SDS-PAGE gave 48 and 53kDa protein bands. The enzyme exhibited serine-protease properties by showing susceptibility to phenyl methyl sulfonyl fluoride, alpha 1-antitrypsin, and egg white and soybean inhibitors. The protease activity in submandibular saliva of caries-resistant subjects was found to be 3.8-fold greater than that in saliva of caries-susceptible individuals, thus suggesting that the enzyme expression may be linked to the resistance to caries.

In isolated, intact liver mitochondria from hyperthyroid rats, the L-glycerol-3-phosphate binding site(s) of the L-glycerol-3-phosphate dehydrogenase was (were) found to be influenced by the nature of the electron acceptor, as well as by the pH and the presence of calcium ions. With the hydrophobic electron acceptor menadione a single L-glycerol-3-phosphate binding site was detected kinetically at bulk pH values between 6.5 and 9.0. With the hydrophilic phenazine methosulfate, on the other hand, two L-glycerol-3-phosphate binding sites were distinguishable at pH > or = 7.5 and pH > or = 7.0, in the presence and absence of Ca2+, respectively. The kinetic mechanism of the reaction catalyzed by L-glycerol-3-phosphate dehydrogenase is ping pong Bi Bi with a hydrophilic electron acceptor, where as with the hydrophobic substance, a sequential Bi Bi mechanism was observed. We suggest that the latter mechanism has physiological relevance.