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Observation of a single tryptic peptide difference, its sequencing and size measurement by mass spectrometry and its mutation to alanine which prevents phosphorylation in vivo, confirm residue serine-15 as the main and probably only region of phosphorylation in yeast hexokinase 2. In vitro phosphorylation is not observed for the alanine-15 mutant enzyme. Serine-15 is part of a protein kinase A consensus phosphorylation sequence.

Saccharomyces cerevisiae strains having only glucokinase as the glucose-phosphorylating enzyme were investigated to elucidate the mechanism of glucose metabolism. The results showed that these strains could accumulate substantial amounts of internal glucose which were not diluted upon provision with external radioactive glucose. In addition, toluene treatment did not reveal much glucokinase activity. These results indicate that glucokinase does not directly limit glucose utilization and that uptake and phosphorylation are linked.

A novel method for studying glucose metabolism in Escherichia coli resting cells was used to determine the effects high fructose-1,6-biphosphate aldolase levels on glucose flux, fructose-1,6-P2 concentration and the equilibration of both its halves. Results revealed that aldolase only slightly influenced these three variables. A fit was demonstrated between the results obtained with resting cells and with the extra enzyme being active. No special assumptions were required to explain the fit, except that the measured Vmax values should underestimate actual values.

In spite of the great importance of mixed electrolytes in science and technology, no compelling theoretical explanation has been offered yet for the thermodynamic behavior of such systems, such as their deviation from ideality and the variation of their excess functions with ionic composition and concentration. Using the newly introduced Smaller-ion Shell treatment - an extension of the Debye- Hückel theory to ions of dissimilar size (hence DH-SiS) - simple analytic mathematical expressions can be derived for the mean and single-ion activity coefficients of binary electrolyte components of ternary ionic systems. Such expressions are based on modifying the parallel DH-SiS equations for pure binary ionic systems, by adding to the three ion-size parameters - a (of counterions), b+ (of positive coions), and b- (of negative coions) - a fourth parameter. For the (+ + -) system, this is "b++," the contact distance between non-coion cations. b++ is derived from fits with experiment and, like the other b's, is constant at varying ion concentration and combination. Four case studies are presented: (1) HCl-NaCl-H2O, (2) HCl-NH4Cl-H2O, (3) (0.01 M HX)-MX-H2O with X = Cl, Br, and with M = Li, Na, K, Cs, and (4) HCl-MCln-H2O with n = 2, M = Sr, Ba; and n = 3, M = Al, Ce. In all cases, theory is fully consistent with experiment when using a of the measured binary electrolyte as the sole fitting parameter. DH-SiS is thus shown to explain known "mysteries" in the behavior of ternary electrolytes, including Harned rule, and to adequately predict the pH of acid solutions in which ionized salts are present at different concentrations. [ABSTRACT FROM AUTHOR]

The almost century-old dispute over the validity of theexperimentallyderived activity of a single ion, ai, is still unsettled; current interest in this issue is nourishedby recent progress in electrochemical cell measurements using ion-specificelectrodes (ISEs) and advanced liquid junctions. Ionic solution theoriesusually give expressions for aivalues of the positive and negative ions, that is, the respective a橷 a–,and combine these expressions to compute the mean ionic activity, a±, that is indisputably a thermodynamicallyvalid property readily derivable from experiment. Adjusting ion-sizeparameters optimizes theory’s fit with experiment for a±through “optimizing” a橷 a–.Here I show that theoretical aivalues thus obtained from the smaller-ion shell treatmentof strong electrolyte solutions [Fraenkel, Mol. Phys.2010, 108, 1435] agree with aivalues estimated from experiment;however, theoretical aivalues derived from the primitive model, the basis of most modernionic theories, do not agree with experiment. [ABSTRACT FROM AUTHOR]