共查询到20条相似文献,搜索用时 31 毫秒
1.
E.M. Kosower 《Biochemical and biophysical research communications》1980,92(2):356-364
A new mechanism that involves dissociative electron transfer in the energy transducing step is set forward for bacterial luciferase catalyzed light emission. The proposal involves (1) dissociation of the 4a-hydroperoxyflavin to a flavin radical and , accounting for 570 and 620nm absorption, (2) addition to the aldehyde carbonyl to form a peroxyl radical, (3) abstraction of H from an enzyme thiol group to form RCH(OOH)OH, (4) thiyl radical abstraction of the H on C in RCH(OOH)OH, a step which can show a of ca. 4, and (5) dissociative electron- transfer, a highly exothermic step that leads to a protonated flavin excited state, a carboxylic acid and water. 相似文献
2.
W M Keung B Holmquist J F Riordan 《Biochemical and biophysical research communications》1980,96(1):506-513
A series of depsipeptides have been synthesized and used to demonstrate the esterase activity of rabbit pulmonary angiotensin converting enzyme. Among the esters studied, Bz-Phe-OPhe-Ala was found to have the highest which is about that of its exact peptide analog, Bz-Phe-Phe-Ala. Esters such as Bz-Gly-OGly-Phe, Bz-Gly-OPhe-Phe and Bz-Gly-OLeu-Ala were also hydrolyzed but at much lower rates. Normal Michaelis-Menten behavior is observed and the kinetic parameters obtained indicate that the esters and their peptide analogs bind to the enzyme equally well, but that peptides are hydrolyzed at much higher rates. Studies on the pH-rate profiles, chloride ion effect, inhibition and chemical modifications detect no mechanistic differences between ester and peptide hydrolysis. 相似文献
3.
Mechanism of action of thrombin on fibrinogen. The reaction of thrombin with fibrinogen-like peptides containing 11, 14, and 16 residues 总被引:4,自引:0,他引:4
J W van Nispen T C Hageman H A Scheraga 《Archives of biochemistry and biophysics》1977,182(1):227-243
The following peptides were synthesized by classical methods in solution: Ac-Gly-Gly- Val-Arg-Gly-Pro-Arg-Val-Val-Glu-Arg-NHCH3 (A), Ac-Ala-Glu-Gly-Gly-Gly-Val- Arg-Gly-Pro-Arg-Val-Val-Glu-Arg-NHCH3 (B), and Ac-Phe-Leu-Ala-Glu-Gly-Gly- Gly-Val-Arg-Gly-Pro-Arg-Val-Val-Glu-Arg-NHCH3 (C). The rates of hydrolysis of the Arg-Gly bond of these three peptides by thrombin were measured, and the values of were found to be 0.05 × 10?7 (A), 0.02 × 10?7 (B), and 1.6 × 10?7 (C) [(NIH units/ liter)s]?1. The value of for peptide C is less than 1% of that for fibrinogen [although the value of kcat itself, for peptide C (but not for A or B), is comparable to that for fibrinogen]. These results indicate that phenylanine and leucine at positions P9 and P8, respectively, play a key role in the reaction of thrombin with fibrinogen. The data also show that factors outside of the 16 residues of peptide C are important in determining the rate of hydrolysis of fibrogen by thrombin. 相似文献
4.
J.Peter H. Burbach Xinchang Wang Marjanne van Ittersum 《Biochemical and biophysical research communications》1982,108(3):1165-1171
Arginine-vasopressin and oxytocin, peptides which serve as putative precursors for neurotrophic fragments, were digested in the presence of the respective 14C-Tyr2- and nonapeptides with a purified synaptic membrane preparation of rat brain. In this preparation aminopeptidase activity predominates in the conversion of these peptides. The disappearance of intact peptide and the release of free 14C-Tyr and 14C-GlyNH2 was followed simultaneously with time by HPLC. Oxytocin was about four times more resistant to proteolysis than arginine-vasopressin as measured by slower disappearance of intact oxytocin, and reflected by the slower release of 14C-Tyr, but not of 14C-GlyNH2 from oxytocin. Comparison of degradation rates of structure analogues showed that peptides having Ile in position 3, as oxytocin, were more resistant than analogues having Phe in position 3, as arginine-vasopressin. The data demonstrate that arginine-vasopressin and oxytocin differ markedly in susceptibility to the aminopeptidase activity in brain synaptic membranes, and indicate that this difference resides primarily in the amino acid residue in position 3. It is suggested that the difference in susceptibility may affect the pattern of neurotrophic metabolites in brain. 相似文献
5.
M. Tegoni J.M. Janot M.C. Silvestrini M. Brunori F. Labeyrie 《Biochemical and biophysical research communications》1984,118(3):753-759
Spectral redox titrations of flavin and cytochrome b2 moieties of flavocytochrome b2 were achieved in the absence and in the presence of pyruvate under equilibrium conditions at 18° C; direct measurements of spin flavosemiquinone proportions have been carried out by EPR determinations at the same temperature. Our results show that the equilibria involving flavin are largely affected by the presence of pyruvate; the semiquinone proportion markedly increases almost till unit near half-reduction of cytochrome b2; at 10 mM pyruvate, the dismutation constant, increases by a factor ≥ 10. 相似文献
6.
The intestinal brush border aminopeptidase and unfractionated maltases are composed of a hydrophilic, sugar containing and enzymatically active part, and a smaller hydrophobic part presumably binding the catalytic part to the lipid matrix of the membrane. Hydrophobic parts detached by trypsin from the detergent forms of aminopeptidase and the maltases were purified and shown to have molecular weights ranging from 8000 to 10000. All rich in hydrophobic residues and contain no disulfide bridges. However, their overall amino acid composition is different. The hydrophobic parts appear to be N-terminal in the detergent forms of the enzymes. 相似文献
7.
Bacillus subtilis aminopeptidase: Specificity toward amino acid amides,dipeptides, and oligopeptides
Mohammed A. Ajabnoor Lee E. Ray Fred W. Wagner 《Archives of biochemistry and biophysics》1980,202(2):540-545
Bacillus subtilis aminopeptidase hydrolyzed amino acid amides with a specificity similar to that determined using amino acyl-β-naphthylamides, but at much greater catalytic rates. Neutral and basic amino acid amides were the best substrates. A series of Leu and Lys NH2-terminal dipeptides hydrolyzed by Co2+-activated aminopeptidase showed that the ratios for the Lys substrates were fourfold greater than the corresponding Leu substrates and that catalytic differences reflected the identity of COOH terminal residues. Greatest catalytic rates were obtained when aromatic residues were in the COOH terminal position of the substrate (Trp, Tyr, Phe); but, significant hydrolysis was achieved when aliphatic residues were COOH-terminal in the dipeptide. The Co2+-activated enzyme would not hydrolyze peptide bonds composed of the imide nitrogen of Pro, thus, bradykinin was not a substrate. However, the Co2+-activated enzyme removed sequentially the first four residues from eledoisin-related peptide and the A chain of bovine insulin. 相似文献
8.
Short, mild treatments of sarcoplasmic reticulum vesicles with aqueous from methanol to caused an inhibition of calcium uptake and an enhancement of ATPase activity. The treatments increased both calcium-dependent (extra) ATPase activity and calcium-independent (basic) ATPase activity of vesicles. The apparent initial reaction rate of ATPase of vesicles was about twice that of control vesicles. With increasing number () of carbon atoms of the , the maximum increment of ATPase activity increased, and both the alcohol concentration () required to inhibit calcium uptake by 50% and the alcohol concentration () required to enhance ATPase activity by 50% of the maximum increment of ATPase activity decreased as follows. The ratio, to , was constant for all values. The apparent free energy of binding of the methylene groups of to sarcoplasmic reticulum vesicles was evaluated (?796 cal/mole) and compared with data from the partition of in octanol and water (?670 cal/mole). The effects of on membrane vesicles are discussed on the basis of these data. 相似文献
9.
Larry J. Takemoto Jeff S. Hansen Bruce J. Nicholson Michael Hunkapiller Jean-Paul Revel Joseph Horwitz 《生物化学与生物物理学报:生物膜》1983,731(2):267-274
A protein of 26 000 has been shown to be the major component of eye-lens junctions, which are similar but not identical to the gap junctions of liver and other tissues. Cyanogen bromide cleavage of the 26 000 polypeptide from bovine lenses yields a major fragment of 15 000 (fragment 1). However, if the junctions are first treated with trypsin or carboxypeptidase Y, cyanogen bromide treatment yields a fragment of reduced molecular weight. Since protease treatment has been shown to cleave residues almost exclusively from the carboxy-terminal end of the 26 000 polypeptide, it follows that fragment 1 represents the carboxy-terminal half of this molecule, part of which is exposed to proteolytic attack outside the membrane. This latter result is corroborated by the fact that antisera which recognize both the 26 000 polypeptide and fragment 1 fail to do so after preadsorption with intact membranes. In addition, comparative amino acid and partial sequence analyses of the 26 000 polypeptide and fragment 1 indicate that fragment 1 is more hydrophilic in character, suggesting that much of the amino-terminal half of the 26 000 polypeptide is buried within the lipid bilayer. 相似文献
10.
If the bicyclic peptide ring proposed by Gross . (1,2) does in fact exist in nisin and related antibiotics, then the unusual β-methyllanthionine component must be significantly distorted from its conformation in the free state, as determined by x-ray structure analysis. The torsion angles about the SCβ bonds are 50–100° from the torsion angles in models of the sulfur-bridged peptide ring proposed for nisin. The chirality of the methylated β-carbon atom is (S). The conformation of the amino acid differs from that of -lanthionine only by a 180° rotation of a carboxyl group about the bond. 相似文献
11.
G W Ruddock J A Raleigh C L Greenstock 《Biochemical and biophysical research communications》1981,102(1):554-560
A steady-state competition system has been developed to investigate the reactions of the superoxide radical anion () with various peroxides, including the so-called Haber-Weiss reaction. Potassium superoxide dissolved in an oxygen-free solution of DMSO containing 18-dicyclohexyl-6-crown, is the source of . High pressure liquid chromatography is used as an assay system for reactivity, to detect and quantitate the yield of anthracene, formed as a major product in the reaction between and 9,10-dihydroanthrancene. Decrease in anthracene yields, in the presence of peroxide, may be used to indicate a possible competing reaction between and added peroxide. Complications involving peroxide-stimulated formation of anthraquinone derivatives are discussed. No evidence for a competing reaction between and peroxide can be detected up to a 10-fold excess of peroxide over 9,10-dihydroanthracene. 相似文献
12.
According to previous authors, cytochrome , when extracted from bovine liver by a detergent method, is called cytochrome . On the other hand, the protein obtained after trypsin action, which eliminates an hydrophobic peptide of about 54 residues, is called cytochrome .Fluorescence polarization of the dansyl phosphatidylethanolamine probe inserted into phospholipid vesicles is very senstive to the binding of proteins, and so is a useful method to study lipid-protein interactions.The chromophore mobility, , decreases markedly when dipalmitoyl phosphatidylcholine vesicles are incubated with cytochrome , whereas does not change for cytochrome and cytochrome . This can be interpreted as a strengthening of the bilayer, only due to the interaction of the hydrophobic peptide tail.Interaction of dipalmitoyl phosphatidylcholine vesicles with cytochrome occurs either below or above the melting temperature of the aliphatic chains (41 °C). Even for a high protein to lipid molar ratio (1 molecule of protein for 40 phospholipid molecules), the melting temperature is apparently unaffected.Phosphatidylserine and phosphatidylinositol do not interact at pH 7.7 with cytochrome , because electrostatic forces prevent formation of complexes. At low pH, the interaction with the protein occurs, but the binding is mainly of electrostatic nature. 相似文献
13.
《Inorganica chimica acta》1986,115(2):169-172
2-(Methylamino)pyridine reacts with RuCl2(CO)3 to give a carbamoyl complex, [)Cl(CO)2], which yields with pyridine (py) and acetylacetone (Hacac), respectively, [)Cl(CO)2(py)] and [)(CO)2(acac)]. These complexes are characterized spectroscopically. The amino group of the ligand is carbonylated and the resulted carbamoyl ligand is chelating through a pyridine ring-N and a carbamoyl-C atom. 2-Aminopyridine and 2-aminopyrimidine react similarly with RuCl2(CO)3 to give the corresponding carbamoyl complexes. 相似文献
14.
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
15.
Twenty-four oligopeptides modeled after the N-terminal portion of the α(A)-chain of human fibrinogen were synthesized and tested as substrates for human thrombin and bovine trypsin. The peptides contained either an Arg-Gly bond, or an Arg-Val bond, or both. Glycine and glutamic acid were substituted at various positions within the peptides, and from the for each peptide with thrombin and with trypsin, the importance of residues on both sides of the Arg-Gly bond was evaluated. The trypsincatalyzed hydrolysis is faster than the thrombin-catalyzed hydrolysis of the peptides with glutamic acid at various distances N-terminal to the Arg-Gly bond. The ratio of the thrombic rate to the tryptic rate is fastest when glutamic acid is six residues away. Thrombin selectively cleaves the Arg-Gly bond in Ac-Val-Arg-Gly-Pro-Arg-Val-OH but cleaves both arginyl bonds rapidly in Ac-Val-Arg-Gly-Pro-Arg-Val-OMe. Trypsin selectively cleaves an Arg-Val bond in Ac-Arg-Gly-Pro-Arg-Val-OMe. The results are discussed in the light of thrombic cleavages of proteins. Most of these are seen to occur at highly polar sequences that frequently contain a proline residue. 相似文献
16.
Joseph Y. Cheung David M. Regen Madge E. Schworer Carol F. Whitfield Howard E. Morgan 《生物化学与生物物理学报:生物膜》1977,470(2):212-229
The kinetic parameters of the sugar transport in avian erythrocytes were evaluated under aerobic and anaerobic conditions. In anaerobic cells, transport measurements with methylglucose resulted in a set of similar dissociation-like constants. Thus the Michaelis constants of methylglucose entry and exit, and , were 8 and 7 mM, respectively. The equilibrium exchange constant, , and the counterflow constant, , were 9 and 11 mM, respectively. The activity constant for transport, , defined as , was 4 ml/h per g. This set of kinetic constants was compatible with a symmetrical mobile-carrier model. In contrast, the Michaelis constant for glucose entry, , was 2 mM and less than the counterflow constant, (8 mM). This result could be accounted for by slower movement of the glucose-carrier complex than the free carrier. The activity constant for glucose transport, , was 5 ml/h perg.Under aerobic conditions, two of the dissociation-like constants ( and ) for transport were significantly larger than those obtained in anaerobic cells, but the remaining two ( and ) remained unchanged. The values, for were 8, 26, 20 and 8 mM, respectively. The activity constant, , decreased to 2 ml/h per g. These changes in kinetic constants were consistent with the hypothesis that anoxia accelerated sugar transport by releasing free carrier that was previously sequestered on the inside of the cell membrane. 相似文献
17.
18.
(1) The polymorphic phase behaviour of aqueous dispersions of various synthetic phosphatidylethanolamines, both singly and in mixtures, has been investigated by 31P-NMR. (2) PE remains in the lamellar phase up to 90°C. PE exhibits a lamellar to hexagonal (HII) transition between 60°C and 63°C. For PE, the lamellar to hexagonal (HII) transition occurs between 7 and 12°C, whereas for PE, the hexagonal (HII) phase is the preferred structure above ?15°C. (3) Mixtures of PE and PE exhibit near-ideal miscibility behaviour. For mixtures of PE and PE there is evidence of fluid-solid immiscibility at temperatures below the gel-liquid crystalline transition temperature of the PE component. Mixtures of PE and PE exhibit complex phase behaviour involving limited fluid-solid immiscibility at low temperatures and formation of a phase allowing isotropic motional averaging at higher temperatures. (4) 31P-NMR provides a graphic method for investigating the miscibility properties of mixed PE systems. 相似文献
19.
Highly purified divalent and monovalent antibodies against cytochrome , anti- immunoglobulin G (IG) and anti- Fab', were used in elucidating the role of this cytochrome in the drug-oxidizing enzyme system of mouse liver microsomes. Anti- IG strongly inhibited not only NADH-supported but also NADPH-supported oxidation of 7-ethoxycoumarin and benzo(a)pyrene, but had no inhibitory action on the oxidation of aniline. Anti- Fab' also inhibited NADH-supported and NADPH-supported benzo(a)pyrene hydroxylation. These observations indicate an essential role of cytochrome in the transfer of electrons not only from NADH but also from NADPH to cytochrome P-450 in the microsomal oxidation of some drugs, but not of aniline. 相似文献
20.
The apparent Arrhenius energy of activation () of the water osmotic permeability () of the basolateral plasma cell membrane of isolated rabbit proximal straight tubules has been measured under control conditions and after addition of 2.5 mM of the sulfhydryl reagent, para-chloromercuribenzenesulfonic acid (pCMBS), of mersalyl and of dithiothreitol. (kcal/mol) was (controls) and (pCMBS), while decreased with pCMBS to of its control value. Mersalyl also decreased both in vitro and in vivo (using therapeutical doses). These actions of pCMBS and mersalyl were quickly reverted with 5 mM dithiothreitol and prevented by 0.1 M thiourea. for free viscous flow is 4.2 and greater than 10 for non-pore-containing lipid membranes. By analogy with these membranes and with red blood cells, where similar effects of pCMBS on are observed, it is concluded that cell membranes of the proximal tubule are pierced by aqueous pores which are reversibly shut by pCMBS. Part of the action of mercurial diuretics can be explained by their action on . 相似文献