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21.
The applicability of microsomal preparations from Drosophilamelanogaster as the metabolic factor in the Salmonella mutagenicity assay with strains TA98 and TA100 was evaluated. Isolated cellular fractions (S27) from PB-pretreated flies activated N-acetyl-2-aminofluorene (2-AAF), N-hydroxy-N-aceyl-2-aminofluorene (N-OH-AAF), benzo[a]pyrene (BP), 9,10-dimethylanthracene (DA) and 2 -naphythylamine (NA)_into mutagenic metabolites, 7,-12-Dimethylbenz[a]-anthracene (DMBA) was ineffective under the conditions of the test.This study was performed in an effort to determine optimal conditions for activating, by Drosophila enzymes, aromatic amines and polycyclic hydrocarbons, with 2-AAF and BP as model mutagens. The following alterations improved the sensitivity of this combined Salmonella/Drosophila assay. (1) Incubation of the plates at 25°C for 1 night instead of permanent exposure at 37°C. (2) Isolation of S27 fractions instead of the conventional S9, because 9000 × g was not sufficient tio spin down Drosphila mitochondria. 相似文献
22.
Using [3H] diazepam as ligand, it is possible to distinguish neuronal binding sites from those present on glial elements and in peripheral tissues (non-neuronal). The function of the "non-neuronal" binding sites is still obscure. Preliminary data showed a distribution of [3H] diazepam binding sites in kidney that could suggest a localization along the renal tubules. This is the site at which a renal peptide, arginine-vasopressin (AVP) is supposed to act. In an attempt to examine the function of these "non-neuronal" sites, we studied the [3H] diazepam binding in kidney of Brattleboro rats which lack AVP and present the symptoms of diabetes insipidus. The homozygous Brattleboro rats showed an increase in the apparent number of benzodiazepine binding sites (Bmax) compared to Long-Evans control rats. Replacement of AVP in these animals results in a reversal of the electrolyte alterations of diabetes insipidus and in an increase of the affinity of the [3H] diazepam binding. These findings may indicate a possible relationship between benzodiazepine binding sites and vasopressin action in kidney and may support receptor function of these "non-neuronal" binding sites. 相似文献
23.
Three experiments demonstrate that inescapable footshock delivered to unrestrained rats produces analgesia as well as performance deficits in subsequent one-way shuttle acquisition. Both the performance and the antinociceptive effects are prevented by pretreatment with as little as 0.1 mg/kg i.p. of the opiate antagonist, naltrexone. These studies suggest that both effects are mediated through opiate receptors with similar underlying naltrexone pharmacodynamics. 相似文献
24.
Mathematical modelling of dynamics and control in metabolic networks. II. Simple dimeric enzymes 总被引:1,自引:0,他引:1
The dynamics of enzyme cooperativity are examined by studying a homotropic dimeric enzyme with identical reaction sites, both of which follow irreversible Michaelis-Menten kinetics. The problem is approached via scaling and linearization of the governing mass action kinetic equations. Homotropic interaction between the two sites are found to depend on three dimensionless groups, two for the substrate binding step and one for the chemical transformation. The interaction between the two reaction sites is shown capable of producing dynamic behavior qualitatively different from that of a simple Michaelis-Menten system; when the two sites interact to increase enzymatic activity over that of two independent monomeric enzymes (positive cooperativity) damped oscillatory behavior is possible, and for negative cooperativity in the chemical transformation step a multiplicity of steady states can occur, with one state unstable and leading to runaway behavior. Linear analysis gives significant insight into system dynamics, and their parametric sensitivity, and a way to identify regions of the parameter space where the approximate quasi-stationary and quasi-equilibrium analyses are appropriate. 相似文献
25.
Endocytosis and degradation of native, cathepsin D-degraded, and glutathione-inactivated aldolase by perfused rat liver 总被引:1,自引:0,他引:1
The uptake and degradation of 125I-labeled (a) native aldolase, (b) cathepsin D-inactivated aldolase, and (c) aldolase inactivated by oxidized glutathione were studied in perfused rat liver. All three forms of aldolase were removed from the perfusion medium and degraded by the liver, but the uptake of the glutathione-inactivated enzyme (half-life in perfusate = 10 min) was much faster than that of the native enzyme (half-life = 30 min) or the cathepsin-inactivated enzyme (half-life = 42 min). The degradation of the enzyme was almost totally inhibited by leupeptin, indicating that thiol proteinases in lysosomes play an important role in the digestion process. Degradation of native and cathepsin D-inactivated aldolase appeared to be slower than that of the glutathione-inactivated enzyme but studies in which liver was preloaded with aldolase by perfusion at 19 degrees C and then warming to 37 degrees C indicated that the rate of degradation of all three forms was similar. It is concluded that the liver is capable of distinguishing between the glutathione-altered aldolase and native or partially degraded aldolase with regard to endocytosis, but that all three forms are degraded at similar rates once within lysosomes. 相似文献
26.
Stuart J. Hamill David Y. Cooper Heinz Schleyer Otto Rosenthal 《Archives of biochemistry and biophysics》1983,224(2):614-624
The time-course kinetics of the cytochrome P-450-catalyzed dealkylations of the exogenous compounds benzphetamine, ethylmorphine, codeine, and 7-ethoxycoumarin were compared to the hydroxylation of the endogenous compound testosterone. Using liver microsomes from phenobarbital-induced rats, the time course of the demethylations of ethylmorphine, codeine, and especially benzphetamine was characterized by a fast initial phase of enzymatic activity and then a steady decline in the rate throughout the remainder of the reaction. In contrast, under the same experimental conditions, both the dealkylation of 7-ethoxycoumarin and the hydroxylation of testosterone showed no initial fast phase of activity and a constant rate of product formation for most of the remainder of the time course. The difference also held for the carbon monoxide inhibition studies in which the degree of inhibition of the demethylation reactions by a variety of CO:O2 mixtures was time dependent, in contrast to the constant, time-independent degree of CO inhibition of the other two reactions. The kinetics of the demethylation reactions could not be explained by enzyme destruction, back reaction, or product adduct formation and were further confirmed by measurements of the rate of O2 utilization and NADPH oxidation. The complexity of the demethylation reaction should be taken into consideration in any detailed studies of the monooxygenation reaction system. 相似文献
27.
Mitogenic response to epidermal growth factor (EGF) modulated by platelet-derived growth factor in cultured fibroblasts 总被引:1,自引:0,他引:1
Walker Wharton Edward Leof Nancy Olashaw E. J. O''Keefe W. J. Pledger 《Experimental cell research》1983,147(2):443-448
The mitotic effects of epidermal growth factor (EGF) were investigated in two cultured fibroblast lines, BALB/c-3T3 and C3H 10T1/2 cells. EGF (30 ng/ml) added to quiescent 3T3 cells in medium containing either platelet-poor plasma or 10(-5) M insulin caused only minimal increases in the percentage of cells stimulated to initiate DNA synthesis. In contrast, EGF acted synergistically with either insulin or plasma to stimulate DNA synthesis in quiescent cultures of 10T1/2 cells, although the maximum effects of EGF were measured at concentrations several-fold greater than those found in either serum or plasma. In either 3T3 or 10T1/2 cells a transient preexposure to platelet-derived growth factor (PDGF) caused over a 10-fold increase in the sensitivity to the mitogenic effects of EGF. It is therefore possible that a primary action of PDGF is to increase the sensitivity of fibroblasts to EGF, independent of whether EGF alone is found to be mitogenic. 相似文献
28.
Experiments to determine the potential of androgen to inhibit estrogen-activated female sexual behavior in rats were conducted. Treatment with either testosterone propionate (0.8 or 1.6 mg/day) or dihydrotestosterone propionate (0.2, 0.4, or 0.8 mg/day) significantly reduced the incidence of lordosis in ovariectomized females receiving estradiol benzoate (1 microgram/day). A similar suppression of estrogen-activated lordosis by testosterone was observed in castrated male rats. Flutamide, an androgen-receptor blocker, prevented the inhibition of lordosis by testosterone in females, indicating that the interaction of testosterone or a metabolite with an androgen receptor may be an important feature of this inhibition. Furthermore, the ability of dihydrotestosterone to inhibit lordosis at lower doses than testosterone suggests that the conversion of testosterone to dihydrotestosterone may also be necessary. These experiments demonstrate the potential of testosterone to inhibit the occurrence of female sexual behavior in rats, in contrast to its established facilitative effect on this behavior. 相似文献
29.
The 13C-n.m.r. spectra of asialo-GM1 and GM1-oligosaccharide are completely assigned and compared to those previously found for intact GM1 and for the series GM4, GM3, GM2, GM1, GD1a, GD1b, and GT1b. Removal of the ceramide residue from GM1 liberated a free, reducing aldehyde group, which was reflected in a doubling of the 13C-n.m.r. signals assignable to the d-glucose residue because of α,β equilibrium. The spectrum of asialo-GM1 lacks the resonances from the sialic acid residue, as expected; in addition, several resonances from the neutral gangliotetraglycosyl residue shifted to different field positions after removal of sialic acid from GM1. These resonances include that of C-4 of the inner β-d-galactosyl residue, and C-1 of the 2-acetamido-2-deoxy-d-galactosyl residue that is near the site of attachment of the sialosyl residue. The differences between the chemical shifts of the carbon resonances of oligomeric and monomeric saccharides, termed linkage shifts, provide a quantitative assignment aid. They are ~ of those for residues linked to sialic acid than those for residues linked to the neutral hexose chain. Correlations among linkage shifts for pairs of glycosidically-linked carbon atoms for asialo-GM1 and GM1-oligosaccharide were compared with those for the series of gangliosides GM4 to GT1b, and differences are noted for resonances for carbon atoms near the sialic acid residue. The spectrum of ganglioside GM1b, a positional isomer of GM1 whose 13C-n.m.r. spectrum has not yet been observed, is predicted. 相似文献
30.
N Kajikawa K Kaibuchi T Matsubara U Kikkawa Y Takai Y Nishizuka K Itoh C Tomioka 《Biochemical and biophysical research communications》1983,116(2):743-750
In platelets, activation of protein kinase C and mobilization of Ca2+ were selectively induced by the addition of 1-oleoyl-2-acetyl-glycerol and a low concentration of A23187, respectively (Kaibuchi, K., Takai, Y., Sawamura, M., Hoshijima, M., Fujikura, T. and Nishizuka, Y. (1983) J. Biol. Chem. 258, 6701-6704). Using this procedure evidence was obtained suggesting that the protein phosphorylation and Ca2+ mobilization were both essential and synergistically effective to cause release of lysosomal acid hydrolases such as N-acetylglucosaminidase. A similar observation was made for the lysosomal enzyme release from rat neutrophils. 相似文献