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111.
C. Dziadik-Turner Daizo Koga Marilyn S. Mai Karl J. Kramer 《Archives of biochemistry and biophysics》1981,212(2):546-560
β-N-Acetylhexosaminidases were detected in 10 insects including species of Lepidoptera, Coleoptera, Hemiptera, and Orthoptera. Two enzymes were purified from the tobacco hornworm, Manduca sexta (L.). EI was detected in larval and pharate pupal molting fluid, integument, and pupal hemolymph while EII was found in larval and pupal hemolymphs. They are acidic hydrolases with similar molecular weights (6.1 × 104), molar extinction coefficients at 280 nm (1.9 × 105 liters mol?1 cm?1), and pH optima (pH 6). They differ in the number of polypeptide chains per molecule (EI is a single chain and EII consists of two polypeptide chains), amino acid composition, extent of glycosylation (EII is probably a glycoprotein), isoelectric point (pIEI = 5.9 and pIEII ~- 5.1), tissue distribution, and reactivities toward nitrophenylated N-acetylglucosamine (kcat,I = 328 s?1 and kcat,II = 103 s?1) and N,N′-diacetylchitobiose (kcat,I = 307 s?1 and kcat,II = 3 s?1). These results suggest that EI is a chitinase and that EII may function as a hexosaminidase in vivo. 相似文献
112.
113.
Videodensitometry based on television technique has been shown to be suitable for recording gel electrophoretic patterns. Its speed of operation is about 60 times as fast as that of conventional densitometers, whereas the patterns recorded are practically the same. 相似文献
114.
Replication complexes containing only one molecule of Q beta replicase and one strand of midivariant RNA (MDV-1 RNA) template were prepared by incubating the replicase with an excess of MDV-1 (-) RNA. In the presence of excess minus strands, these monoenzyme replication complexes were shown to synthesize essentially pure MDV-1 (+) RNA in both the first and second cycles of replication. When an equivalent concentration of mutant MDV-1 (-) RNA was added to this reaction before completion of the first cycle of replication, only wild-type MDV-1 (+) RNA was produced in the first cycle, but both mutant and wild-type MDV-1 (+) RNA were produced in the second cycle of replication. These results demonstrate that a monoenzyme complex is competent to synthesize RNA and, therefore, that a multienzyme replication complex is not a necessary intermediate of replication. The data also imply that after the completion of chain elongation, the product strand is released from the replication complex and that the template and the replicase then dissociate. 相似文献
115.
116.
Studies were carried out to investigate the effects of prostaglandins (PG) in vitro on adrenal microsomal steroid and drug metabolism in the guinea pig. The addition of PGE1, PGE2, PGA1, PGF1 alpha or PGF2 alpha to isolated adrenal microsomes produced typical type I difference spectra. The sizes of the spectra (delta A385-420) produced by prostaglandins were smaller than those produced by various steroids including progesterone, 17-hydroxyprogesterone and 11 beta-hydroxyprogesterone. However, the affinities of prostaglandins and steroids for adrenal microsomal cytochrome P-450, as estimated by the spectral dissociation constants, were similar. Prior addition of prostaglandins to isolated adrenal microsomes did not affect steroid binding to cytochrome P-450 or the rate of steroid 21-hydroxylation. In contrast, prostaglandins inhibited adrenal metabolism of ethylmorphine and diminished the magnitude of the ethylmorphine-induced spectral change in adrenal microsomes. The results indicate that prostaglandins inhibit adrenal drug metabolism by interfering with substrate binding to cytochrome P-450. Since 21-hydroxylation was unaffected by PG, different cytochrome P-450 moieties are probably involved in adrenal drug and steroid metabolism. 相似文献
117.
Primycin, an antibiotic active against Gram-positive microorganisms increased the permeability ofBacillus subtilis cell membranes when used in bacteriostatic concentrations. On addition of the antibiotic to the washed cell suspension, a dose-dependent increase in the conductivity was observed. Furthermore, an enhanced leakage of the nucleotides (measured by the32P-ATP release from the32P-labelled culture) could be detected.To get more information about the mechanism of the primycin-membrane interaction, the effect of the antibiotic on the ATPase activity of membrane vesicles prepared from bothBacillus subtilis andEscherichia coli B was studied. Activation was found at about 0.5 nmol antibiotic/g protein and its extent was approximately the same as with sonicated membranes used as controls. Stimulation of ATPase activity was also achieved with vesicles prewashed with 3 mM Tris-HCl buffer.Purified membrane ATPase fromBacillus subtilis could not be activated by primycin at all; above 0.3 nmol/g protein concentration the enzyme was inhibited. When acting on membrane vesicles isolated fromEscherichia coli B, inhibition without previous activation was observed, although sonication caused a substantial activation on the ATPase of these membranes.These observations confirmed our suggestion that the primary target of primycin action is the cell membrane in Gram-positive microorganisms.Abbreviations OD
Optical density 相似文献
118.
John W. Greiner Robert E. Kramer Howard D. Colby 《Prostaglandins & other lipid mediators》1979,17(4):587-597
Studies were carried out to investigate the effects of prostaglandins (PG) on adrenal microsomal steroid and drug metabolism in the guinea pig. The addition of PGE1, PGE2, PGA1, PGF1α or PGF2α to isolated adrenal microsomes produced typical type I difference spectra. The sizes of the spectra (ΔA385–420) produced by prostaglandins were smaller than those produced by various steroids including progesterone, 17-hydroxyprogesterone and 11β-hydroxyprogesterone. However, the affinities of prostaglandins and steroids for adrenal microsomal cytochrome P-450, as estimated by the spectral dissociation constants, were similar. Prior addition of prostaglandins to isolated adrenal microsomes did not affect steroid binding to cytochrome P-450 or the rate of steroid 21-hydroxylation. In contrast, prostaglandins inhibited adrenal metabolism of ethylmorphine and diminished the magnitude of the ethylmorphine-induced spectral change in adrenal microsomes. The results indicate that prostaglandins inhibit adrenal drug metabolism by interfering with substrate binding to cytochrome P-450. Since 21-hydroxylation was unaffected by PG, different cytochrome P-450 moieties are probably involved in adrenal drug and steroid metabolism. 相似文献
119.
The two membranes, plasmalemma and tonoplast (Saccharomyces cerevisiae H 1022), are characterized ultrastructurally by their different texture in the corresponding freeze-fracture faces and their silver staining properties.Biochemical characterization with regard to proteins and lipids indicated that the ratio of protein to lipid is significantly higher in the plasmalemma as compared to the tonoplast. Moreover, a pronounced difference appears to exist for both the amount and the composition of total lipids, phospholipids and sterols. The protein patterns of the plasmalemma and the tonoplast reveal only minor differences, as judged by sodium dodecyl sulphate gel electrophoresis. 相似文献
120.
The antitumor agent BCNU (1,3-bis(2-chloroethyl)-1-nitrosourea) was incubated with poly(C) and poly(G) in aqueous solution at 37 degrees and pH 7 to produce approximately 0.33 and 0.07% substitution, respectively. Under the same conditions, there was relatively little reaction with poly(A) and poly(U). Poylnucleotides reacted with [14C]BCNU were digested by chemical and enzymatic methods, and the derivative nucleotides were isolated by column chromatography. There were identified by a combination of ultraviolet and mass spectroscopy as 3-(beta-hydroxyethyl)CMP, 3,N4-ethano-CMP, and 7-(beta-hydroxy-ethyl)GMP. This would indicate that BCNU generates active two carbon fragments, probably chloroethyl carbonium ions, which are free to react with nucleotides. The production of these substituted bases may be important to the mechanism of action of the therapeutic nitrosoureas since they would probably alter the function of any nucleic acid which contained them. 相似文献