Enzymes activated by monovalent cations

Theoretical studies of metal-phosphate interactions: interaction of Li+, Na+, K+, Be++, Mg++, and Ca++ with H2PO4- and (CH3O)2PO2-: implications for nucleic acid solvation

Model phosphate-metal solvation complexes have been studied by ab-initio self-consistent-field techniques. The complexes studied include (RO)2PO2-(R = H or CH3) with Li+, Na+, K+, Be++, Mg++, Ca++, H2O, and Cl-. The geometries of the complexes were chosen to approximate reasonable model solvation complexes for phosphate groups in a nucleic acid environment. Calculated energies of formation vary as Be++ greater than Mg++ greater than Ca++ greater than Li+ greater than Na+ greater than K+ for all isostructural complexes, consistent with experimental binding trends. These results suggest that site binding of this type can successfully account for the relative specificities of ion binding in polynucleotides and other phosphate-containing molecules.

Protein hydration changes during catalysis: a new mechanism of enzymic rate-enhancement and ion activation/inhibition of catalysis

There exists a linear correlation between the effect of a salt on the rate of an enzymic reaction and its effect on the activation volume (delta V++) of the reaction. Salts that increase delta V++ invariably decrease the rate of the reaction, and vice versa. The salt effects on reaction rate are, however, much larger than would be predicted solely on the basis of pressure-volume work changes deriving from the observed alterations in delta V++. Different inorganic salts affect reaction rates and activation volumes in a manner that reflects the salts' positions in the Hofmeister series. These observations, taken in conjunction with data on the effects of salts on protein functional group (aminoacid side-chains and peptide linkages) hydration, lead us to propose the following hypothesis to account for salt activation and inhibition of catalysis. Aminoacid side-chains and peptide linkages located on or near the protein surface change their exposure to water during conformational events in catalysis. These protein group transfers are accompanied by large volume and energy changes that are due largely to changes in the organization of water around these groups. When these transfer processes occur during the rate-limiting step in catalysis, these energy and volume changes can contribute to the free energy of activation (delta G++) and the activation volume of the reaction. By influencing the degree to which water can organize around transferred protein groups, salts can modify both the delta G++ (rate) and the delta V++ of a reaction.

Integrative recombination of bacteriophage lambda DNA in vitro

An in vitro system for the production of integrative recombinant DNA of bacteriophage lambda is described. The in vitro recombination mimics the in vivo integration of viral DNA into host DNA in its requirement for int gene product, for the presence of a thermolabile component, and for the limitation of the recombination to a pair of specialized sites (attachment sites) on the DNA. The enzymes are extracted from Escherichia coli containing phage lambda gene products. The substrate is the DNA from lambda-attB-attP, a phage variant that contains two attachment sites on the same chromosome. The product is a recombinant phage chromosome that has lost the DNA between the attachment sites. The parental and recombinant DNA are distinguished following transfection to mature phage in spheroplasts. The reaction requires ATP, Mg++, spermidine, and a monovalent cation. Recombination occurs preferentially between attachment sites on the same molecule. The enzymatic activity is completely inhibited by extracts containing xis gene product.

Ion levels and membrane potential in chick heart tissue and cultured cells

Intracellular concentrations of sodium and potassium as well as resting potentials and overshoots have been determined in heart tissue from chick embryos aged 2-18 days. Intracellular potassium declined from 167 mM at day 2 to 117-119 mM at days 14-18. Intracellular sodium remained nearly constant at 30-35 mM during the same period. The mean resting potential increased from -61.8 mV at day 3 to about -80 mV at days 14-18. The mean overshoot during the same period increased from 12 to 30 mV. P(Na)/P(K) calculated from the ion data and resting potentials declined from 0.08 at day 3 to 0.01 at days 14-18. Thus, the development of embryonic chick heart during days 2-14 is characterized by a declining intracellular potassium concentration and an increasing resting potential and overshoot. Heart cells from 7- to 8-day embryos, cultured either in monolayer or reassociated into aggregates, were compared with intact tissue of the same age. The intracellular concentrations of sodium and potassium were similar in the three preparations and cultured cells responded to incubation in low potassium medium or treatment with ouabain in a manner similar to that of intact tissue. Resting potentials and overshoots were also similar in the three preparations.

Partial purification and some properties of the uridine diphospho-N-acetylglucosamine-enolpyruvate reductase from Staphylococcus epidermidis

A method for the partial purification of the uridine diphospho-N-acetylglucosamine-enolpyruvate reductase from Staphylococcus epidermidis is presented. Some properties of the enzyme, including its dependence on monovalent cation and flavine adenine dinucleotide, are discussed.