NMR titration curves are reported for the 4 histidine residues of ribonuclease A in sodium acetate and for ribonuclease S in sodium acetate, phosphate, and sulfate solutions. Evidence is presented that the imidazole side chain of histidine residue 48 undergoes a conformational change, probably also involving the carboxyl side chain of aspartic acid residue 14. This group is considered to be res...

The effect of pH on steady state kinetic parameters for the yeast alcohol dehydrogenase-catalyzed reduction of aldehydes and oxidation of alcohols has been studied. The oxidation of p-CH3 benzyl alcohol-1,1-h2 and -1,1-d2 by NAD+ was found to be characterized by large deuterium isotope effects (kH/kD = 4.1 plus or minus 0.1) between pH 7.5 and 9.5, indicating a rate-limiting hydride trahsfer st...

It has been proposed (Creutz, C. E., Pazoles, C. J., and Pollard, H. B. (1978) J. Biol. Chem. 253, 2858-2866) that synexin, an adrenal medullary protein that causes Ca2+-dependent aggregation of isolated chromaffin granules, might be the intracellular receptor for Ca2+ in the process of exocytosis. We now report that Ca2+ interacts directly with isolated synexin, inducing rapid self-association...

Acid-base titration experiments and electrostatic force microscopy (EFM) were used to investigate the cell surface electrochemical heterogeneity of the Fe(III)-reducing bacteria, Shewanella putrefaciens. The acid-base titrations extended from pH 4 to 10, and the titration data were fit using a linear programming pKa spectrum approach. Overall, a five-site model accounted for the observed titrat...

C . T. KAPPAGODA, R. J. LINDEN, H. M. SNOW AND J. B. STOKER, Cardiovascular Unit, Department of Physiology, The University, Lee&, 6 August 1973 In an attempt to decide on a clinically acceptable method of assessing the metabolic component of the acid-base status of blood, Lewis & Stoddart [Clinical Science (1973) 44, 297-3001 compared two indices of the non-respiratory state of blood in vivo. T...

The titration curves of the human hemoglobins AZ and F, the slow and fast components of horse hemoglobin, and bovine hemoglobin B have been analyzed, mainly to obtain information about the titration behavior of the histidines in these hemoglobins. The results were also compared with earlier data concerning human hemoglobin A and bovine hemoglobin A. In both hemoglobin As and F, 18 titratable hi...