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131.
T. T. Tchen Samuel W. Chan Tuan H. Kuo K. M. Mostafapour Victoria H. Drzewiecki 《Molecular and cellular biochemistry》1977,15(2):79-87
Summary Biochemical and ultrastructural studies indicate that the atrophy of adrenal cortex in hypoyhysectomized rats involves the following changes: (1) One to two days after hypophysectomy, there is loss of template activity resulting from cumulative DNA-damage and heterochromatinization.In vivo ACTH-administration led to recuperation of these cells, indicating damage during hypophysectomized state to be reversible. (2) If the duration of hypophysectomy is prolonged, some of the cells become irreversibly damaged and can no longer recuperate afterin vivo ACTH administration. (3) The period of most rapid cell death is from the third to seventh day after hypophysectomy. The cause of cell death is probably due to membrane damage in the absence of protein synthesis, leading to lysis of the cells. Lysozomes and macrophages are apparently not involved.Supported by U.S.P.H.S. grants AM-5384 and AM-13724 and taken in part from dissertations submitted by Chan and by Mostafapour to Wayne State University in partial fulfillment towards the Ph.D. degree.An invited article. 相似文献
132.
Native aspartate transcarbamoylase from Escherichia coli was modified with the bifunctional reagent tartaryl diazide in the presence of the substrate carbamoyl phosphate and the substrate analog succinate. The product had the same sedimentation coefficient as the native enzyme but showed a marked increase in affinity for the substrate aspartate with a hyperbolic saturation curve. The Michaelis constant for aspartate (7.4 mM) is similar to that estimated for the relaxed state of the enzyme. The high substrate affinity was not produced if modification was conducted in the absence of substrate analogs or with a monofunctional reagent. The modified enzyme was also desensitized towards the allosteric effectors ATP and CTP. It appears to represent a stabilized relaxed state whose conversion to the taut state is presumably prevented by cross-linking. 相似文献
133.
The structure and the orientation of cytochrome c oxidase molecules in crystalline cytochrome c oxidase membranes (Vanderkooi, G., Senior, A.E., Capaldi, R.A., and Hayashi, H. (1972) Biochim. Biophys. Acta 274, 38-48) were studied by image analysis of electron micrographs and by reacting the crystalline preparations with immune gamma-globulins against individual cytochrome c oxidase subunits. Binding of gamma-globulins to the membranes was detected by the following two methods: (a) electrophoretic identification of gamma-globulin polypeptides in the washed membranes; (b) electron microscopic examination of the negatively stained membranes. The membranes bound immune gamma-globulins against subunit IV (which faces the matrix side in intact mitochondria) but failed to bind immune gamma-globulins against subunits II + III (which face the outer side of the inner membrane in intact mitochondria). In contrast, solubilized cytochrome c oxidase bound either of the two immune gamma-globulins. All cytochrome c oxidase molecules in the crystalline membranes are thus asymmetrically arranged so that subunit IV faces outward and subunits II + III face toward the interior. This orientation is opposite to that found with intact mitochondria. The data also suggest that the crystalline membranes form closed vesicles which are impermeable to externally added gamma-globulins. 相似文献
134.
Membrane protein synthesis in embryonic chick erythroid cells 总被引:4,自引:0,他引:4
135.
Association of long surface appendages with adherence-related functions of the gram-positive species Actinomyces naeslundii 总被引:18,自引:3,他引:15
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Electron microscopy of new isolates of gram-positive Actinomyces naeslundii demonstrated long, fragile appendages. Removal of the appendages impaired attachment to epithelial cells and reaggregation, thus implicating them in attachment-related functions. 相似文献
136.
Antibiotic activity against Heliothis virescens was found in flower buds of Gossypium hirsutum, experimental stock Texas 254. Relatively low antibiotic activity was found in hexane extract, high activity in methanolic extract and residue, and no activity in acetone and water extracts. A condensed tannin having a molecular weight of 4850 was isolated from methanolic extract by column chromatography on Sephadex G-25. It was the major antibiotic component, 3.4% of the dried flower bud. The condensed tannin at 0.2% in the diet retarded larval growth by 84%. 相似文献
137.
Rats weighing 100 g were made chronically uremic by partial left renal artery ligation and contralateral nephrectomy. Rats with urea clearances below 0.30 ml/min and sham-operated controls were pair-fed arginine-free diets, diets containing normal amounts of arginine or diets with high levels of arginine. After 4 to 8 weeks, rats were killed and plasma levels of arginine, ornithine and lysine were measured. In addition, activities of various urea cycle enzymes in liver and kidney and renal transamidinase were determined. Plasma amino acid levels and enzyme activities of the urea cycle remained constant in control rats fed diets differing in arginine content. However, renal transamidinase activity was elevated in control rats fed arginine-free diets. In plasma of uremic as compared with control rats, arginine levels varied with the arginine intake, and lysine levels were elevated when arginine supplements were fed. With all diets, plasma ornithine remained constant in uremic rats at slightly but not significantly increased levels. Hepatic carbamoyl phosphate synthetase activity and renal arginine synthetase activity were reduced in uremic as compared to control rats. Renal transamidinase activity, expressed per g of kidney, was elevated in uremic rats with all diets except arginine-free. When amino acid diets were fed, hepatic arginase activity was higher in uremic rats and this increase was enhanced by arginine-free diets. Other enzyme activities in uremic rats were not affected by the amount of arginine in the diet. 相似文献
138.
The interaction of cortisol and progesterone with pure transcortin was investigated. The temperature dependence of cortisol and progesterone binding is a result of the predominantly negative enthalpy of binding which suggests a very good fit between ligand and protein such that the bonds formed are of the van der Waals type. The optimal pH of cortisol (8.0) and progesterone (8.5) binding suggests involvement of cysteine, histidine, and/or tyrosine residues in the binding process. Transcortin is irreversibly denatured at pH 4.0. The effect of sodium chloride on the binding of both steroids is small. At lower sodium chloride concentrations (less than 0.15 m), binding decreases somewhat with decreasing salt concentration. Urea produces a progressive decrease in the association constants of both steroids which is completely reversible up to 2.0 m and 30% reversible at 3.0 m. Scatchard analysis of cortisol binding in the presence of a constant amount of progesterone and vice versa confirms earlier data obtained on plasma that cortisol and progesterone do not bind at two independent sites. It is not possible, however, to decide whether they bind at the same site or at two interdependent (interacting) sites. 相似文献
139.
M Z Fan W Y Chan G Griesmann O M Rennert 《Physiological chemistry and physics and medical NMR》1983,15(1):81-87
The fate of exogenously added 14C-putrescine following incubation for 24 hours with McCoy and human skin fibroblast cultures was examined. The nature of the polyamine derivatives found were quite different indicative of a difference in the cellular metabolism of polyamines. Exogenously added putrescine (PUT) was metabolized by both McCoy and human skin fibroblast cultures to form spermidine (SPD), spermine (SPM), gamma-aminobutyric acid (GABA) and some unidentified compounds. Within the experimental period of observation, human cultured fibroblasts metabolized PUT more efficiently than McCoy cells and converted more than 50% of it into SPD, SPM, GABA and unknown compounds. Monoacetyl putrescine (MAP) was formed by human skin fibroblasts. It was mainly identified in the culture medium. No MAP was detectable either intracellularly or extracellularly in McCoy cultures. The percentage of 14C-radioactivity found as PUT in the culture medium was greater in McCoy cells (86.0%) than in human fibroblasts (53.9%). The reverse was true for the percentage distribution of 14C-radioactivity as PUT inside the cells. No low Mr conjugates of SPD or SPM were found in the medium or intracellularly with either culture type. Some low Mr putrescine conjugates were found in the culture media; these were identified by the liberation of PUT upon acid hydrolysis. 相似文献
140.
Direct effect of glucose on the preproinsulin mRNA level in isolated pancreatic islets 总被引:17,自引:0,他引:17
The effects of glucose on the preproinsulin mRNA level and the rate of (pro)insulin biosynthesis were examined in isolated mouse pancreatic islets. Relative concentrations of preproinsulin mRNA were quantitated by a RNA-dot hybridization procedure. The level of preproinsulin mRNA in islets incubated for up to 7 days at 20 mM glucose remained constant. In islets incubated at 3.3 mM glucose the preproinsulin mRNA level decreased and was after 24 h reduced to one tenth of the level at 20 mM glucose. Subsequent incubation at 20 mM glucose completely restored the preproinsulin mRNA level but only after 3 days of culture, while the insulin release was restored within 24 h. The insulin-biosynthetic activity of the islets was correlated to the variation in the level of the preproinsulin mRNA. These results suggest that glucose does have a direct influence on the level of preproinsulin mRNA and that the rate of (pro)insulin biosynthesis is limited by the level of the preproinsulin mRNA. 相似文献