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1.
2.
Neutrophil myeloperoxidase from a patient with chronic myelocytic leukemia was isolated under conditions designed to minimize proteolysis. Those methods yielded an α2β2 form of myeloperoxidase from normal individuals. Purified enzyme from the patient had electronic absorbances (), enzymatic activity, and electrophoretic and Chromatographic behavior indistinguishable from that of normal myeloperoxidase. Edman degradation and physical studies after reduction and denaturation, however, showed that as compared to normal enzyme, one 55,000-dalton α subunit of the patient's myeloperoxidase was replaced by a 39,000-dalton peptide with a different amino-terminal sequence, a mixture of smaller peptides, and an heme derivative. Myeloperoxidase from the leukemic neutrophils appeared to have been partially degraded in vivo by lysosomal proteases. 相似文献
3.
Inhibitors of glutamine synthetase cause derepression of nitrogenase biosynthesis in the presence of in the photosynthetic bacterium Rhodopseudomonas capsulata. A new derepressor of nitrogenase biosynthesis, β-N-oxalyl-L-α,β-diaminopropionic acid (ODAP), is here compared with the widely used L-methionine-DL-sulfoximine (MSX). With both compounds, a quantitative correlation has been observed between inhibition of glutamine synthetase and derepression of nitrogenase biosynthesis. We also find that both MSX and ODAP inhibit nitrogenase activity in vivo in R. capsulata. The latter effect seems to be indirect and related to the previously reported reversible inhibition of nitrogenase activity in vivo by . As a control it was observed that neither nor MSX nor ODAP inhibit nitrogenase activity in vivo in Clostridium pasteurianum. 相似文献
4.
R C Warrington 《Analytical biochemistry》1974,62(1):204-216
A general procedure for the isolation of 3′-linked fragments derived from tRNA molecules is described. Purified N-2-naphthoxyacetylglycyl derivatives of the and of yeast were exhaustively digested with RNase T1 and the 3′-linked fragments (bearing the derivative) were separated from other degradation products (lacking the derivative) by stepwise chromatography on BD-cellulose. Subsequent chromatographic resolution and base-composition analysis allowed tentative identification of the 3′-terminals of and as Gp(Cp,Ap)CpCpA and Gp(Cp,Cp,Up,Ap)CpCpA, respectively. The potential utility of this procedure for development of a novel approach to nucleic acid sequence analysis is discussed. 相似文献
5.
M.Alfonsina Desiderio Angela Sessa Antonio Perin 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1985,845(3):463-468
The administration of preferential adrenergic receptor antagonists to uninephrectomized rats revealed the mediation in diamine oxidase activity increase that occurs in the remaining kidney undergoing compensatory hypertrophy. In fact, or , but not , , or this enzyme enhancement. Further studies with adrenoceptor agonists, such as epinephrine (, , , ), isoproterenol (, ) or terbutaline () showed that also in normal rat kidney diamine oxidase activity is under the control of through a mechanism that involves new synthesis of mRNA and protein. Theophylline, an inhibitor of phosphodiesterase, or forskolin, an activator of adenyl cyclase, increased diamine oxidase activity as does epinephrine or nephrectomy. Thus, catecholamine-triggered coupled to adenyl cyclase are involved in the regulation of diamine oxidase activity in normal and hypertrophic rat kidney. 相似文献
6.
Bacterial bioluminescence-identification of fatty acid as product, its quantum yield and a suggested mechanism 总被引:5,自引:0,他引:5
By using radioactive decanal the direct transformation of this aldehyde to decanoic acid, with a quantum yield of 0.13, has been demonstrated. A mechanism analogous to that of other better understood bioluminescent reactions is proposed, leading to a product, as yet unisolated from the enzymic reaction, whose fluorescence spectrum is an excellent match for that of the luminescence.The extensive examination1,2,3 of the isolated bacterial luminescence system has resulted in the accepted outline shown. We wish to modify it, in accordance with the previous evidence, by suggesting that ’intermediates I and II‘ in Hastings' terminology2 are the same enzyme bound FMNH2 moiety. A lively controversy has surrounded the attempts to determine whether aldehyde exerts a purely catalytic role2 or is transformed in the reaction.4 If the aldehyde reacts, then the simplest product is the corresponding carboxylic acid, perhaps formed via the peracid. The most likely alternative reaction would involve enolistation and oxidation at the α-methylene group. We examined the second alternative fairly carefully, and found no evidence for it. We do not wish to report these results in detail at present, since we have now established that the acid corresponding to that formed in a normal autoxidation of the aldehyde is the product. Some indication of the nature of the products of the reaction is available.5Since the amount of product in the reaction is restricted to a very low level by the concentrations required, we labelled decanal with tritium at C-2 and thus were able to record the yield with some precision. Although recent work6 strongly implies that acid is formed stoichiometrically, the direct measurement of the quantum yield with respect to acid formation is necessary before a mechanism can be written. We have suggested a mechanism compatible with observations in this system, analogous to all cases of bioluminescence for which a mechanism is reasonably well established. This mechanism also leads to a product excited state with excellent agreement around pH7 in fluorescence wavelength to that of the luminescence. 相似文献
7.
An enzyme isolated from Agrobacterium radiobacter was shown to catalyse the following reaction: Some properties of this new enzyme, acid amidohydrolase, are presented in this paper. The potential application of this enzyme for the preparation of some d-amino acids used as pharmaceutical intermediates is discussed. 相似文献
8.
F. Peter Guengerich David P. Ballou Minor J. Coon 《Biochemical and biophysical research communications》1976,70(3):951-956
Stopped flow spectrophotometry has shown the occurrence of two distinct spectral intermediates in the reaction of oxygen with the reduced form of highly purified cytochrome P-450 from liver microsomes. As indicated by difference spectra, Complex I (with maxima at 430 and 450 nm) is rapidly formed and then decays to form Complex II (with a broad maximum at 440 nm), which resembles the intermediate seen in steady state experiments. In the reaction sequence, P-450LMredComplex I→Complex II→P-450LMox the last step is rate-limiting. The rate of that step is inadequate to account for the known turnover number of the enzyme in benzphetamine hydroxylation unless NADPH-cytochrome P-450 reductase or cytochrome is added. The latter protein does not appear to function as an electron carrier in this process. 相似文献
9.
The kinetic α-secondary deuterium isotope effect, , for the pH-independent hydrolysis of nicotinamide riboside, yielding nicotinamide and ribose, in water at 25 ° is 1.14, establishing that this reaction proceeds with unimolecular substrate decomposition to yield a carboxonium ion, or related species, in the rate-determining step. Surprisingly, the corresponding isotope effect for the base-catalyzed decomposition of the same substrate is 1.12, a value indicating considerable sp2 character at the Cl′ position in the transition state for this reaction. A similar result, , was obtained for base-catalyzed hydrolysis of NAD+. The kinetic alpha deuterium isotope effect for the pig brain NAD glycohydrolasecatalyzed hydrolysis of nicotinamide riboside is 1.08. This value suggests that CN bond cleavage to form an intermediate carboxonium ion, or structurally related species, is at least partially rate-determining. In contrast, the corresponding value for the hydrolysis of this substrate catalyzed by Escherichia coli nicotinamide ribonucleotide glycohydrolase is very near unity, a result consistent with several interpretations including a rate-determining enzyme isomerization reaction. 相似文献
10.
The kinetic parameters for the hydrolyses of different l-α-amino acid-β-naphthylamides by Bacillus subtilis aminopeptidase have been measured for the native enzyme and for the enzyme activated in 5 mm Co(NO3)2. In most cases Co2+ activation decreased Km(app) values and increased kcat values, in other cases km(app) and kcat values were increased; for the remainder of the substrates tested km(app) values and kcat values were decreased. In all cases tested the ratios of were increased (2- to 108-fold). For the native enzyme the order of specificity toward the l-amino acid-β-naphthylamides was Arg > Met > Trp > Lys > Leu and for the Co2+ activated enzyme the order of specificity was Lys > Arg > Met > Trp > Leu. The native enzyme hydrolyzed Pro-β-naphthylamide, but not α-Glu-β-naphthylamide; Co2+ activation of the enzyme affected an appreciable rate of hydrolysis of the latter substrate. 相似文献
11.
Initial velocity measurements were made on the ribonuclease A catalyzed hydrolysis of P-5′-Urd-2′:3′-P in the pH range 4.0–8.0 at 25 °C in 0.1 m Tris-acetate/0.1 m KCl. The pH dependence of the Michaelis constant, Km, the turnover number ks, and for P-5′-Urd-2′:3′-P were similar to those reported for Urd-2′:3′-P (5). When P-5′-Urd-2,3-P and Urd-2′:3′-P were compared under similar conditions the average difference in ks and Km indicated that these parameters were 5-fold and 23-fold lower, respectively, for P-5′-Urd-2′:3′-P. The slight difference in the pH dependence of for these two substrates can be interpreted in terms of a specific interaction of the enzyme at the 5′ position of P-5′-Urd-2′:3′-P, which permits a less exclusive dependence on the ionized state of the free enzyme in binding this substrate. The nature of the interaction of the substrate 5′-phosphomonoester group with the enzyme is discussed in terms of possible interactions with Lys-41 and His-119. 相似文献
12.
The biosynthesis of blood group B determinants by the blood group A gene-specified alpha-3-N-acetyl-D-galactosaminyltransferase 总被引:1,自引:0,他引:1
The blood group gene-specified α-3-N-acetyl-D-galactosaminyl-transferase in human plasma, when concentrated by adsorption onto group O red cell ghosts or Sepharose 4B, catalyses the transfer of D-galactose in α-linkage to low-molecular-weight H-active acceptors. The product synthesised with 2′-fucosyllactose is chromatographically indistinguishable from the blood group B-active tetrasaccharide, Galα1→3[Fucα1→2]Galβ1→4Glc. The optimum pH for the transfer of D-galactose by the -transferase is 7. At this pH the Vmax for the transfer of N-acetyl-D-galactosamine is about 300 times higher than that for the transfer of D-galactose. These results indicate that an -transferase can, under centain conditions, synthesise B determinant structures. 相似文献
13.
P Valenzuela P Bull J Zaldivar A Venegas J Martial 《Biochemical and biophysical research communications》1978,81(2):662-666
Ovine mammary gland mRNAs were translated in a wheat-germ cell-free system in the presence of radioactive amino acids. Automated Edman degradation performed on α-lactalbumin isolated by immunoprecipitation from the mixture of radiolabelled lactoproteins showed the occurrence of an hydrophobic 19 residues long amino terminal extension. The pre-protein represents the primary translation product since the amino terminal methionyl residue was found to be donated by initiator . Comparison of the signals of ovine α-lactalbumin and hen's egg white lysozyme, two homologous proteins which are thought to be derived from a common ancestor, suggests that the signal region has evolved at least as rapidly as the remaining part of the polypeptide chain. 相似文献
14.
A simple procedure for resolution of Escherichia coli RNA polymerase holoenzyme from core polymerase. 总被引:32,自引:0,他引:32
The association constant, KA, for myosin subfragment-1 binding to actin was measured as a function of ionic strength [KCl, LiCl, and tetramethylammonium chloride (TMAC)]and temperature by the method of time-resolved fluorescence depolarization. The following thermodynamic values were obtained from solutions of 0.20 × 10?6m S-1, 1.00 × 10?6m actin in 0.15 m KCl, pH 7.0, at 25 °C: ΔG ° = ?39 ± 1 kJ M?1, ΔH0 = 44 ± 2 kJ M?1 and . For measurements in KCl (0.05 to 0.60 m), In . Thus, the binding is endothermic and strongly inhibited by high ionic strength. When KCl was replaced by LiCl or TMAC the ionic effects on the binding were cation specific. The nature of actin-(S-1) binding in the rigor state is discussed in terms of these results. 相似文献
15.
High avidity antisera against β-endorphin were obtained in two of five rabbits immunized with unconjugated synthetic human . One of these antisera (K-7762) cross-reacted 1.5% on a molar basis with β-lipotropin and did not recognize leucine-enkephalin in a concentration as high as 0.2 mmol/l. The cross-reaction with methionine-enkephalin was 9%, while that with α-endorphin ( 61–76) was 69%. This implied that the specific recognition site was in the amino-terminal region of . Although this sequence is present in it was poorly recognized by the antiserum, suggesting that the free amino-terminal is essential. This interpretation was supported by the finding that was equally poorly recognized by the antiserum. The sensitivity of the radioimmunoassay was 1.9 pmol/l. was not detectable (< 3 pmol/l) in 26 of 27 extracted plasma samples in healthy blood donors, in one it was 5 pmol/l. In five of six patients with an enlarged sella turcica, but without clinical and laboratory evidence of pituitary dysfunction, was detectable (; mean ± S.D.) after metyrapone. was elevated in Addison's disease (23, 54 and 76 pmol/l), Nelson's syndrome (37, 39 and 109 pmol/l), ectopic ACTH production (27, 59 and 76 pmol/l), but only detectable in one of three samples from patients with Cushing's disease (7 pmol/l). Gel chromatography of extracts of porcine pituitary revealed only one immunoreactive peak co-eluting with synthetic human . The specificity of the antiserum K-7762 was such that the concentration in plasma extracts could be reliably estimated by radioimmunoassay without prior chromatography. 相似文献
16.
The structural changes accompanying the recently described sub-transition of hydrated dipalmitoylphosphatidylcholine (Chen, S.C., Sturtevant, J.M. and Gaffney, B.J. (1980) Proc. Natl. Acad. Sci. USA 77, 5060–5063) have been defined using X-ray diffraction methods. Following prolonged storage at ?4°C the usual Lβ′ gel form of hydrated dipalmitoylphosphatidylcholine (DPPC) is converted into a more ordered stable ‘crystal’ form. The bilayer periodicity is 59.1 Å and the most striking feature is the presence of a number of X-ray reflections in the wide angle region. The most prominent of these are a sharp reflection at and a broader reflection at . This diffraction pattern is indicative of more ordered molecular and hydrocarbon chain packing modes in this low temperature ‘crystal’ bilayer form. At the sub-transition (Trmsub = 15–20°C) an increase in the bilayer periodicity occurs () and a strong reflection at approx. with a shoulder at approx. is observed. This diffraction pattern is identical to that of the bilayer gel (Lβ′) form of hydrated DPPC. Thus, the sub-transition corresponds to a bilayer ‘crystal’ → bilayer Lβ′ gel structural rearrangement accompanied by a decrease in the lateral hydrocarbon chain interactions. Differential scanning calorimetry and X-ray diffraction show that on further heating the usual structural changes Lβ′ → Pβ′ and Pβ′ → Lα occur at the pre- and main transitions, at approx. 35°C and 41°C, respectively. 相似文献
17.
H B Stuhrmann M H Koch R Parfait J Haas K Ibel R R Crichton 《Journal of molecular biology》1978,119(2):203-212
Neutron small-angle scattering of the 70 S Escherichia coli ribosomes and of its smaller 30 S subunit has been measured in mixtures. A linear dependence of the square of the radius of gyration on the reciprocal of the contrast is found, which is qualitatively similar to the results from contrast variation with the larger 50 S subunit. The slope α in this plot is a measure of radial segregation of RNA and proteins. It is most pronounced with the 50 S subunit. The 30 S particle appears to be more homogeneous, whereas the 70 S ribosome assumes an intermediate value of α. Neither the 30 S and 50 S subunits nor the 70 S ribosome show a significant separation of the centres of mass of their RNA part and proteins. A quantitative comparison of the parameters obtained suggest that the interaction between the two subunits and the 70 S ribosomes does not involve any major change in the latter. 相似文献
18.
An investigation of the effect of PGF2α induced parturition alone or in combination with neostigmine (NEO) on subsequent productivity was conducted in a total confinement swine production unit. Forty-five crossbred gilts and 106 sows were randomly assigned to one of six treatments: (1) , (2) , (3) , (4) , (5) , (6) . PGF2α injections (IM) were given 2 days prior to the mean expected farrowing day for this farm (day 112). NEO injections (IM) were given after the fourth pig born in gilt litters and after the fifth pig born in sow litters. Females injected with 0 or 10 mg PGF2α farrowed 71.7 ± 3.7 and 31.4 ± 3.4 hours after treatment, respectively (P<0.01). No other parameters measured were significantly affected by injection of PGF2α. These data show that PGF2α effectively induced parturition and did not adversely affect subsequent litter productivity. NEO was found to be ineffective in reducing total farrowing time (P>0.05). 相似文献
19.
E W Miles 《Biochemical and biophysical research communications》1975,64(1):248-255
α-Cyanoglycine inactivates the pyridoxal-P forms of the β2 subunit and the α2β2 complex of tryptophan synthase; an intense chromophore at 430 nm forms concomitantly. The slow reactivation of the modified β2 subunit upon dialysis () is prevented by addition of α subunit, which presumably acts by changing the environment of the chromophoric derivative. These data and the observed protection from inhibition by L-serine indicate that α-cyanoglycine acts as a substrate analog which undergoes a second, largely irreversible reaction at the active site of the β2 subunit. Modification of the β2 subunit increases its affinity for the α subunit. Modification of the α2β2 complex increases its stability to heat, urea, and low pH. 相似文献
20.
Robert J. Blagrove Glenn G. Lilley Albertus Van Donkelaar Samuel M. Sun Timothy C. Hall 《International journal of biological macromolecules》1984,6(3):137-141
Molecular weights and sedimentation coefficients have been measured for different oligomeric forms of phaseolin, the major storage protein in seeds of Phaseolus vulgaris L. The results indicate that phaseolin is a trimer () at neutral pH which aggregates further to a dodecamer form () at pH 4.5. The subunit size is in good agreement with the recently determined sequence molecular weight, if allowance is made for bound oligosaccharide and phytic acid moieties. The trimeric nature at neutral pH has been confirmed by chemical crosslinking studies using dimethylsuberimidate and dithiobis(succinimidylpropionate). Analyses of optical rotatory dispersion and circular dichroism data have been used to examine the corformation of phaseolin. In common with other seed globulins, a low proportion of α-helix () coupled with a high level of β-sheet () is predicted. These data are compared with a structural analysis based on the amino acid sequence of a phaseolin subunit polypeptide. The predicted level of α-helix is increased () when phaseolin is heated in sodium dodecyl sulphate, but not when the detergent is added at room temperature. 相似文献