George I. Drummond

Abstract Experiments were performed on adenyl cyclase in washed particles of guinea pig ventricle and in particulate preparations extracted with LiBr. The Km for ATP was 0.08 mm. Since one Mg++ binds with ATP at pH 7.5, it was concluded that the true substrate is a Mg-ATP complex. Concentrations of Mg++ as high as 10 mm were required to saturate the enzyme; the Ka for this cation was 2 to 3 mm. Mg++ saturation curves were sigmoidal. Mg++ did not affect the Km for ATP. It was concluded that Mg++ binds to a second and possibly allosteric site. The consequence of this binding is significantly increased reactivity of the catalytic site for substrate. Fluoride profoundly activated the enzyme even in the presence of saturating amounts of Mg++ and was without significant effect on the affinity of ATP or of Mg++ for their binding sites. It was concluded that F- binds to the enzyme possibly as a magnesium-fluoride complex, the consequence of which is greater reactivity of the catalytic site than that produced by Mg++ alone. This activating effect was specific for F-; a variety of anions and organic fluorine compounds were inactive. The enzyme was activated by catecholamines but to a much lower degree than by F-. Ca++ was inhibitory both in the presence and absence of F-; the inhibitory action of Ca++ was found to be competitive with respect to Mg++. A Ki of about 0.3 mm for Ca++ was obtained. The possibility is considered that Mg++, by binding to a site other than the catalytic site, might serve in physiological regulation of the enzyme and that Ca++ by binding at this site may also have a modulating action.

Studies on a 2′,3′-cyclic nucleotide-3′-phosphohydrolase are presented. Bovine brain white matter was fractionated by differential centrifugation and sucrose density gradient techniques. The phosphohydrolase was distributed throughout all primary fractions: nuclear, mitochondrial, and microsomal. When these fractions were subjected to sucrose density gradient centrifugation the enzyme appeared only in the myelin-containing layers. Brains of newborn rats were essentially devoid of phosphohydrolase activity and the content rose rapidly during the 12th and 25th days, coinciding precisely with the development of myelin. Mutant 'quaking' mice whose brains are partially deficient in myelin were also partially deficient in enzyme activity. The data provide evidence that the phosphohydrolase is associated with myelin.The enzyme opens the cyclic phosphodiester linkage of Ap(Ap) 2 A cyclic P and Ap(Ap) 6 A cyclic P without rupture of internucleotide bonds. The enzyme also hydrolyzed the 2′,3′-cyclic phosphorothioates of uridine and guanosine. The K m for adenosine 2′,3′-cyclic phosphate was determined to be 1.9 × 10 −3 M, an inordinately high value, and since nothing is known about the physiological role of the enzyme, the possibility is raised that the true substrate may not be a cyclic nucleotide.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCyclic Phosphates. IV.1 Ribonucleoside-3',5' Cyclic Phosphates. A General Method of Synthesis and Some PropertiesM. Smith, G. I. Drummond, and H. G. KhoranaCite this: J. Am. Chem. Soc. 1961, 83, 3, 698–706Publication Date (Print):February 1, 1961Publication History Published online1 May 2002Published inissue 1 February 1961https://pubs.acs.org/doi/10.1021/ja01464a039https://doi.org/10.1021/ja01464a039research-articleACS PublicationsRequest reuse permissionsArticle Views743Altmetric-Citations160LEARN 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