Showing papers on "Conformational change published in 1969"
TL;DR: This finding suggests that the reactivity of the —SH group is dependent exclusively on the presence of the ligand on the β chains, and is independent of the state, liganded or not, of the α chains.
92 citations
TL;DR: The effect of ATP suggests a conformational change due to simple binding of ATP to the membrane, similar to that of ATP, which was obtained with ADP, ITP and by increasing the pH of the membrane suspension above 9.1.
69 citations
TL;DR: Proton relaxation rate studies provided evidence for a second substrate induced conformational change on the addition of l-arginine to the ternary MnADP-enzyme complex and small but probably significant differences in the properties of the two enzymes were indicated.
Abstract: Proton relaxation rate studies have been used to study the interaction between arginine kinase from two sources, Homarus vulgaris and Homarus americanus, and manganous ion, MnADP- and MnATP2-, respectively. There was negligible interaction between Mn2+ and the H. vulgaris enzyme but a small effect with the H. americanus enzyme. In both cases, a large enhancement of the proton relaxation rate was seen on the addition of ADP or ATP to a solution containing Mn2+ and enzyme. It was concluded that the enzyme combines with MnADP− or MnATP2- rather than with Mn2+.
Enhancements of the proton relaxation rate of the ternary complexes, MnADP-E (45), Mn2′-dADP-E (28) and MnATP-E (17), were obtained with the H. vulgaris arginine kinase and Mn3′-dADP− and Mn2′-dATP2- were also demonstrated to form ternary complexes with this enzyme. For arginine kinase from H. americanus, values for MnADP-E (17), Mn2′-dADP-E (approx. 12) and MnATP-E (approx. 8) were determined. A comparative kinetic study demonstrated reasonable agreement between the kinetically determined Km values and dissociation constants from the proton relaxation rate data. It was also found that for both enzymes, there was a correlation between the enhancement and maximum velocity values, ADP > 2′-dADP and ATP > 2′-dATP which could be interpreted as indicative of a graded degree of substrate induced conformational change. The proton relaxation rate and kinetic studies indicated small but probably significant differences in the properties of the two enzymes.
Proton relaxation rate studies provided evidence for a second substrate induced conformational change on the addition of l-arginine to the ternary MnADP-enzyme complex. No significant effect was observed with d-arginine, which is a competitive inhibitor with respect to l-arginine.
24 citations
TL;DR: A decrease of the optical rotation in the wavelength region from 200 to 250 mμ is observed when ligands bind to hemoglobin, interpreted as being caused by a small conformational change, which influences the electronic transitions of a number of peptide bonds or (and) a few aromatic side chains.
Abstract: A decrease of the optical rotation in the wavelength region from 200 to 250 mμ is observed when ligands bind to hemoglobin. The change at 233 mμ amounts to about 8% of the total rotation at this wavelength, independently of the nature of the ligand (O2, CO, NO or ethyl-isocyanide). The effect is interpreted as being caused by a small conformational change, which influences the electronic transitions of a number of peptide bonds or (and) a few aromatic side chains. The change is observed with αβ-dimers, but not with the isolated single chains. The full effect is present however, in chemically modified hemoglobins which no longer show cooperative interactions in the ligand equilibrium curve. It is speculated that the conformational change takes place within the protomers but only when these are joined in αβ-dimers (or tetramers). The chemical modifications might not prevent the initial ligand-induced conformational change, but only abolish the transmission of the conformational change from one subunit to the others.
23 citations
TL;DR: Fluorescein mercuric acetate has been shown to be a highly selective reagent for suppressing the energized to energized-twisted configurational transition of heavy beef heart mitochondria as determined by electron microscopy and by measurement of light scattering changes.
19 citations
TL;DR: Temperature dependence studies on the competitive water analogue inhibitors of α-chymotrypsin show that complex formation is independent of temperature and that binding is primarily entropy-driven, and it is suggested that the aliphatic alcohol and ketone may well bind at a slightly different site or portion of the enzyme than that with which the aromatic inhibitors combine.
16 citations
TL;DR: ACh-ase by hydrolyzing ACh permits the receptor to return to its original conformation; the barrier of the ion movements is thereby re-established.
Abstract: Publisher Summary This chapter discusses the structure and function of the enzyme acetylcholinesterase (ACh-ase). The enzyme is a dimer, each protomer comprising two nonidentical chains. The nonidentity of the two groups of polypeptide chains is supported by the determination of the number of active sites of ACh-ase. The α-chain of ACh-ase contains an active site. The α and β chains together may form an active unit. Acetylcholine (Ach) is released by excitation in the excitable membranes as a specific signal and causes a conformational change of the ACh receptor, thereby releasing Ca 2+ ions bound to carboxyl groups of the protein. Ca 2+ ions are involved in the excitability of nerve and muscle fibers; the Ca 2+ ions released induce conformational changes of phospholipids and other polyelectrolytes. Thus, these reactions act as typical amplifiers of the signal given by ACh. ACh-ase by hydrolyzing ACh permits the receptor to return to its original conformation; the barrier of the ion movements is thereby re-established.
15 citations
TL;DR: The observed 7- fold increase in catalytic rate coupled with the concomitant 6-fold increase in the rate of alkylation strongly suggests that the binding of methylguanidine to the recognition site of the enzyme alters the reactivity of an imidazole group (groups).
12 citations
TL;DR: In this paper, the temperature dependence of the electron paramagnetic resonance (EPR) spectra of spin-labeled intact vacuoles was investigated with spin-and fluorescence-labeling techniques.
12 citations
01 Jan 1969
TL;DR: In this article, the states of association of β-lactoglobulins are discussed, with particular emphasis on the mechanism of the pH 4-5 low temperature octamer formation.
Abstract: Summary The states of association of the β-lactoglobulins are discussed, with particular emphasis on the mechanism of the pH 4–5 low temperature octamer formation. The bell-shaped pH dependence of this reaction is explained, linking it to a small conformational change observed in the same pH range. The physico-chemical properties of this protein are examined in terms of the allosteric model and it is proposed that β-lactoglobulin is a good model of subunit allosteric enzyme systems.
8 citations
TL;DR: Optical rotatory dispersion and circular dichroism measurements were carried out on a block copolymer, (γ‐ethyl DL‐glutamate)160 (L‐Trp)32, in which the tryptophan sequence has been modified to various extents by using 2‐nitrophenylsulfenyl chloride, and the assumption was made that no conformational change occurs on proceeding from the pure unmodified tryptophile sequence to the completely modified sequence.
Abstract: Optical rotatory dispersion (ORD) and circular dichroism (CD) measurements were carried out on a block copolymer, (γ-ethyl DL-glutamate)160 (L-Trp)32, in which the tryptophan sequence has been modified to various extents by using 2-nitrophenylsulfenyl chloride. The CD spectrum of the completely modified copolymer exhibits bands in some of the regions of maximum absorption of the sidechain chromophores. In the peptide absorption region the spectrum is similar to that reported in the literature for polypeptides in the α-helical conformation. When the extent of modification of the tryptophan sequence is progressively reduced, there is a gradual change in the ORD spectra of the copolymers. On the basis of these data the assumption was made that no conformational change occurs on proceeding from the pure unmodified tryptophan sequence to the completely modified sequence. The results are discussed in connection with the study of possible conformational effects arising from selective chemical modification of tryptophan residues in proteins.
TL;DR: Tritium-hydrogen exchange and optical rotation have been used to detect possible conformational changes of the E. coli isoleucyl-tRNA synthetase in the presence and and absence of substrates and it is found that the substrates induce a conformational change in the enzyme.
TL;DR: The storage of hen egg-white lysozyme solutions in the cold does not affect the enzyme-catalyzed lysis of Micrococcus lysodeikticus cells or the hydrolysis of chitin oligosaccharides.