The study of the temperature dependence of the hydrolysis of cytidine 2′,3′‐phosphate by bovine pancreatic ribonuclease A (EC 3.1.27.5) at pH 7.0 by using the pH‐stat method showed a transition at 4 C [J. A. Biosca and C. M. Cuchillo (1980) Biochem. J. 189, 655–6571, The breaks found in the Van't Hoff and Arrhenius plots at pH 7.0 were confirmed in the present work by following the reaction spectrophotometrically with a stopped‐flow spectrophotometer adapted to the use of sub‐zero temperatures. Similar results were found at pH 5.5. In addition it was found that the discontinuity disappears when 40% ethyleneglycol is present in the reaction mixture. However, in this latter instance a discontinuity around 0°C appears in the Arrhenius plot. To explore the possibility that all these effects were due to a conformational transition in the protein, thermal perturbation experiments were carried out with the enzyme. A change in the slope of the plot of as a function of temperature was found around 6°C at pH 7.0 but not at pH 5.5. The results reported here can be interpreted as due to a change in the protein structure induced by the change of the structure of water. The studies carried out in the presence of ethyleneglycol also open the way to the cryoenzymological experimentation on ribonuclease.
Incubation of rat neural lobes with heavy meromyosin (HMM) after prolonged glycerination, induced characteristic arrowhead decoration of a number of microfilaments at different levels of the neurosecretory axons. In non terminal sections of axons the labelled microfilaments showed preferential relationships with microtubules in addition to occasional contacts with the axolemma and various axonal organelles. In axonal endings, they were mainly associated to microvesicles and appeared to be anchored on the axolemma facing the perivascular space at the level of membranous densifications.
The ATPases of activated and relaxed rabbit psoas myofibrils were studied by the rapid flow quench method in a solvent of near physiological pH and ionic strength. Both types of myofibrils bind and hydrolyze ATP with transient kinetics very similar to those found with myosin. But the kcat of activated myofibrils was 100× that with the relaxed myofibrils. Relaxed myofibrils and myosin could not be distinguished kinetically.
Abstract Abstract Proteins play a key role in the metabolism of living organisms as, for example, catalysts (enzymes), carriers or receptors of various molecules. These marginally stable biopolymers of amino acids can be perturbed in their activity by pressure, temperature and other environmental variables as organic solvents. Changing environmental conditions can induce metabolism dysfunctions. On isolated systems, i.e. purified proteins, high pressure and other perturbing variables can be used as tools for investigation of protein structure/activity relationships and enzyme mechanisms. The elementary basic physical mechanisms of the action of high pressure upon proteins are stated in the first part of this review. This is followed by a section devoted to technical aspects, including methods for generation of high pressure, and some recent developments, namely stopped-flow spectrometry and electrophoresis under high pressure. Then, the use of pressure as a tool for investigation of enzyme mechanisms and for study of protein equilibria (isomerization, association/dissociation, interaction with other molecules) is exposed. In conclusion, the biotechnological potentialities of high pressures are briefly evoked. Key Words: Hydrostatic pressuresubzero temperaturessolvent effectelectrophoresisenzymesfast reactions
pK values of ionisation of cytidine residues, in poly C and poly I. poly C, have been determined by potentiometric titration as a function of either ionic strength (Na+) or Mg2+ concentra- tion.The results are interpreted as a consequence of the exis- tence of a local pH, prevailing in the vicinity of the polynucle- otides, smaller than that of the bulk solution.This local pH is dependent upon the electrostatic potential T due to the nega- tively charged phosphate groups of the polynucleotide.Moreover T can be modulated through variation of either ionic strength or Mg2+ concentration.At a given pH Mg2+ addition leads to the release of protons which, in the case of complex systems of limi- ted stability, might be detected by the use of the pH-stat method.Possible functional implications for genetic translation systems are examined.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCalcium-activated myofibrillar ATPase: transient kinetics and the titration of its active sitesM. Houadjeto, F. Travers, and T. BarmanCite this: Biochemistry 1992, 31, 5, 1564–1569Publication Date (Print):February 11, 1992Publication History Published online1 May 2002Published inissue 11 February 1992https://pubs.acs.org/doi/10.1021/bi00120a038https://doi.org/10.1021/bi00120a038research-articleACS PublicationsRequest reuse permissionsArticle Views44Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)