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N Jentoft

Publications and source records attributed to N Jentoft.

24 records · Page 2Linked to original sources
PubMed1982

Intramolecular interactions of amino groups in 13C reductively methylated hen egg-white lysozyme.

Reductive methylation of hen egg-white (HEW) lysozyme with [13C]formaldehyde and NaCNBH3 and subsequent 13C NMR spectroscopy reveal resonances for each of the mono- and dimethyl derivatives of the six lysyl epsilon-amino groups and the NH2 terminus. Each resonance has a unique chemical shift, pKa, and chemical shift change upon deprotonation. The assignment of the resonances arising from the N alpha,N-dimethyl and N alpha-monomethyl NH2 terminus has been made as have resonance assignments for the two lysyl residues which crystallographic studies indicate are involved in ion pair interactions (Imoto, T., Johnson, L. N., North, A. C. T., Phillips, D. C., and Rupley, J. A. (1972) in The Enzymes (Boyer, P. D., ed) 3rd Ed, Vol. 7, pp. 665-868, Academic Press, New York). One resonance, tentatively assigned to the lysine 1 (epsilon NH3+) which forms an ion pair with glutamic acid 7 (gamma COO-), has a highly perturbed chemical shift which shows a biphasic titration curve (N epsilon, N-dimethyl pKa values 10.0 and 2.6). A similar titration curve is observed for a N epsilon-monomethyl lysyl residue. The resonance for lysine 13 (epsilon NH3+), which forms an ion pair with the carboxyl terminus, leucine 129 (alpha COO-), has been assigned by removal of leucine 129 with carboxypeptidase whereupon only one pair of mono- and dimethyl lysyl resonances is greatly perturbed. The pKa of N epsilon,N-dimethyl lysine 13 is 9.3 in des-Arg-Leu-lysozyme in contrast to 9.8 for the intact enzyme. Thus, it appears that both of the intramolecular ion pairs predicted by x-ray crystallography exist in the solution structure of HEW lysozyme.

Amino Acids↗
PubMed1981

[13C]Methylated ribonuclease A. 13C NMR studies of the interaction of lysine 41 with active site ligands.

A unique resonance in the 13C NMR spectrum of [13C]methylated ribonuclease A has been assigned to a N epsilon, N-dimethylated active site residue, lysine 41. The chemical shift of this resonance was studied over the pH range 3 to 11, and the titration curve showed two inflection points, at pH 5.7 and 9.0. The higher pKa, designated pKa1, was assigned to the ionization of the lysyl residue itself while the pKa of 5.7, designated pKa2, was assigned on the basis of its pKa to the ionization of a histidyl residue which is somehow coupled to lysine 41. Both pKa values are measurably perturbed by the binding of active site ligands including nucleotides, nucleosides, phosphate, and sulfate. In most cases, the alterations in pKa values induced by the ligands were larger for pKa2. The ligand-induced perturbations in pKa2 generally paralleled those reported for histidine 12, another active site residue (Griffin, J. H., Schechter, A. N., and Cohen, J. S. (1973) Ann. N. Y. Acad. Sci. 222, 693-708). The sensitivity of the N epsilon, N-dimethylated lysine 41 resonance to the histidyl ionization may result from a conformational change in the active site region of ribonuclease which is coupled to the histidyl ionization. This coupling between lysine 41 and another ribonuclease residue, which has not been documented previously, offers new insight into the interrelationship between residues in the active site of this well characterized enzyme.

Animals↗
PubMedDate not supplied

Viscoelastic properties of solutions of ovine submaxillary mucin.

The linear viscoelastic and rheological properties of high molecular weight ovine submaxillary mucin (OSM) solution have been investigated in terms of the Newtonian steady-flow viscosity [eta(gamma)], the complex oscillatory viscosity [eta*(omega)], and the storage and loss shear moduli [G'(omega) and G"(omega)]. It was observed that tau(gamma), eta*(omega), and G'(omega) are always higher when OSM is dissolved in 0.1M NaCl than when at the same concentration in 6M GdnHCl. This is consistent with previous observations that submaxillary mucins self-associate in 0.1M NaCl to form large aggregates, which are disrupted in 6M GdnHCl. As the OSM concentration increases, the appearance of a plateau shear modulus indicates the formation of a gel network in both solvents. The results suggest gelation involves specific intermolecular interactions, perhaps due to hydrophobic forces between interdigitated oligosaccharide side chains. The viscoelastic behavior of OSM solution at high concentration is thus similar to that reported in the literature for porcine gastric mucin (PGM). However, the OSM gels are mechanically weaker, having moduli that are an order of magnitude lower than those for PGM gels of comparable concentration. The oligosaccharide side chains of OSM consist of only 1-2 sugar units compared to 10-15 for PGM, but it appears that this is sufficient to allow for intermolecular interaction and the formation of weak gels.

Animals↗