Daniel E. Atkinson

Adenine nucleotide concentrations and turnover rates. Their correlation with biological activity in bacteria and yeast.

Publisher Summary The chapter reviews the correlations, both stoicheiometric and regulatory, that have been reported between the concentrations of the different adenine nucleotides and the occurrence or rates of integrated functions such as growth or production of storage compounds. The roles of the adenine nucleotides may be conveniently classified under three headings. First, they are intermediates in the biosynthesis of nucleic acids and histidine, and also of nucleotide cofactors such as Nicotinamide adenine dinucleotide (NAD), Nicotinamide adenine dinucleotide phosphate (NADP), flavin adenine dinucleotide (FAD), and coenzyme A. Second, they constitute an energy-transducing system that stoicheiometrically couples all metabolic processes and thus plays the central role in stoicheiometric correlation of metabolism. Third, they kinetically regulate the activities of a large number of enzyme reactions and probably of all metabolic sequences. In serving as intermediates, the adenylate do not differ in principle from dozens of other compounds, but the second and third functional categories are unique. Metabolism is organized around the adenine nucleotides and these compounds must be taken into account in the study of nearly every aspect of functional biology. It has become apparent that the associated role of these nucleotides in kinetic correlation and regulation is equally unique, ubiquitous, and important. All metabolic pathways are stoicheiometrically related through the adenine nucleotide system, because all either utilize or regenerate ATP. It is a logical necessity, if these sequences are to be mutually regulated so as to maintain biological homeostasis, that all sequences must also be kinetically regulated, directly or indirectly, by the same coupling system.

Limitation of Metabolite Concentrations and the Conservation of Solvent Capacity in the Living Cell

Publisher Summary This chapter discusses the limitations of the metabolite concentrations and the conservation of solvent capacity in the living cell. The maintenance of low concentrations of metabolites may well be the most pressing problem of metabolic control. Several features of metabolism and of metabolic enzymes appear to represent adaptations to the need to limit solute concentrations and to conserve solvent capacity. Conservation of low concentrations of metabolites, both individually and collectively, is one of the most fundamental requisites for a viable metabolizing system. If concentrations of intermediates are to be kept low, it is necessary that the Michaelis constant of each enzyme involved in a sequence has an appropriate value and that the activity of each enzyme is high enough to handle the maximal flux through the sequence without the substrate concentration rising much above this Michaelis value. The activation of metabolic intermediates, coordinate derepression, or induction contributes to stability and survival through aiding in the conservation of low concentrations within the cell.

The Role of Urea Synthesis in the Removal of Metabolic Bicarbonate and the Regulation of Blood pH

Publisher Summary The rates of reactions, the conformations of macromolecules, the interactions among macromolecules and between macromolecules and ligands of low molecular weight, and virtually everything that exist or occur in a living cell are affected by pH. The maintenance of intracellular pH within a reasonably narrow range should be among the most important and difficult regulatory necessities in living organisms. The problem is particularly acute in microorganisms, with their very large surface/mass ratios. In multicellular animals, the regulation of pH has been generalized and in some sense simplified by transferring it from the individual cells to systemic control systems that stabilize the pH of blood and extracellular fluid. The cells of mammals, for example, have become so dependent on this stabilization of the pH of their surroundings that an increase or decrease of 0.5 pH unit seriously threatens the life of the organism. One of the most important biological advantages of the development of a closed circulation by metazoans is that individual cells are freed from the necessity to produce the machinery needed for the stabilization of pH, osmolarity, and ionic strength against wide external fluctuations and the need to expend large amounts of ATP to effect this stabilization.

Kinetics of regulatory enzymes: effect of adenosine triphosphate on yeast citrate synthase.

Abstract We have suggested ( Hathaway and Atkinson, 1963 ) that modulation of the kinetic behavior of DPN-specific isocitrate dehydrogenase by AMP is part of a complex control system by which the utilization of acetyl coenzyme A (AcSCoA) for fat production is regulated in response to the momentary energy needs of the cell. This proposal suggested the possibility that the alternative fate of AcSCoA—entry into the citric acid cycle—might be under complementary control. This paper presents evidence that the kinetic properties of the appropriate initial enzyme, citrate synthase [citrate oxaloacetate-lyase (CoA-acetylating) EC 4.1.3.7] are directly modulated by changes in ATP concentration within the physiological range.

The role of ureagenesis in pH homeostasis

Abstract Catabolism of protein liberates HCO 3 − , which cannot be eliminated in the necessary amounts through the lungs, kidneys, or intestines, and thus poses a threat of alkalosis to air-breathing animals. That threat is met by biosynthetic sequences that consume the weak acid NH 4 + and liberate its proton for reaction with HCO 3 − . Different kinds of air-breathing animals use different syntheses for this purpose; mammals utilize ureagenesis. Modulation of the rate of urea synthesis in response to pH is an important part of the interacting regulatory systems by which pH homeostasis is maintained in mammals.

Adenine nucleotides as universal stoichiometric metabolic coupling agents.

Summary The adenine nucleotides participate in every extended metabolic sequence, and thus serve as stoichiometric coupling agents linking all of the chemical activities that constitute life. Each metabolic sequence may be assigned an ATP coupling coefficient—the number of molecules of ATP regenerated (or used) when a mole of substrate is degraded or a mole of product formed. The ATP coupling coefficient for any metabolic conversion is an evolved phenotypic characteristic of the organism, and it determines the thermodynamically feasible direction of conversion under physiological conditions. Thus the unidirectionality of metabolic sequences is a direct consequence of the values of their ATP coupling coefficients. Using these coupling coefficients, “prices,” expressed in ATP equivalents, may be assigned to metabolites. Metabolism may thus be viewed as a problem in the allocation of resources. This approach may be pedagogically useful in focusing attention on metabolic interrelation-ships, rather than on individual sequences for their own sakes. It also explains the need for universal kinetic control of metabolic sequences by the energy charge of the adenine nucleotide pool.

The inhibition of citrate synthase by adenosine triphosphate

Abstract 1. 1.Citrate synthase (citrate oxaloacetate-lyase (CoA-acetylating), EC 4.1.3.7) has been partially purified from beef liver, beef heart and Escherichia coli . The beef heart and beef liver enzymes were quite similar in their pH optima, substrate affinities and sensitivity to ATP inhibition. The E. coli enzyme had a lower substrate affinity and had a lower K i for ATP than the mammalian enzymes. The E. coli citrate synthase differed markedly from the mammalian enzymes in its response to pH changes. 2. 2.ATP was competitive with respect to CoASAc with the beef liver and beef heart enzymes. In E. coli , ATP was not competitive with CoASAc but changed both V and K m for oxaloacetate. Mg + also inhibits the activity of the E. coli citrate synthase and tends to relieve the ATP inhibition. 3. 3.The ATP inhibition of citrate synthase may act in concert with AMP and ADP stimulation of isocitrate dehydrogenase and with citrate stimulation of CoASAc carboxylase in partitioning CoASAc between oxidation by way of the citric acid cycle and storage as fat. It may also play a role in regulating liver ketone body formation.

QUANTITATIVE METHOD FOR DETERMINATION OF INDOLE, TRYPTOPHAN, AND ANTHRANILIC ACID IN THE SAME ALIQUOT.

Abstract The Ehrlich method for the determination of indole-like compounds was expanded by the appropriate control of acidity and oxidation to differentiate between anthranilic acid, indole, and tryptophan. This method afforded a convenient quantitative determination of these three compounds in the same aliquot. This determination depends upon the reactions of anthranilic acid and indole with p -dimethylaminobenzaldehyde (PDAB) in 0.5 N acid to form colored products. The formation of a colored derivative of tryptophan with PDAB requires the presence of much higher acid concentration (ca. 11 N ) and an oxidizing agent. The color formation does not appear to be affected by the presence of constituents of a synthetic Lactobacillus medium.

Response of nucleoside diphosphate kinase to the adenylate energy charge

Abstract The reaction catalyzed by nucleoside diphosphate kinase responds to the energy charge of the adenylate pool. The velocity is maximal at a charge of 1.0, and decreases sharply with a decrease in the charge. This response may control the flow of phosphate from ATP into the other nucleotide pools and thus participate in the regulation of macromolecular synthesis by the energy level of the cell, as reflected in the charge of the adenylate pool.

Comparison of some physical and chemical properties of eight strains of tobacco mosaic virus

Abstract The isoelectric points, ultraviolet absorption spectra, and electrophoretic mobilities between pH 4.15 and 8.0 of eight strains of tobacco mosaic virus are presented. The results confirm an earlier classification of these strains into four groups. Some of the differences in ultraviolet spectra and in slope of the mobility-vs-pH curves are correlated with differences in tyrosine, tryptophan, and histidine content. Strains within a group do not differ in any of the properties determined. Infrared absorption spectra of all strains are essentially identical.