Proton magnetic resonance study of the histidines in hemerythrin and chemical identification of the nonligand histidines

Abstract

Three non-iron-liganded histidines have been studied in methemerythrin azide monomers from Pascolopsis gouldii by 250-MHz proton correlation nuclear magnetic resonance (NMR) spectroscopy. Four of the seven histidines in the protein are not observed because of paramagnetic broadening by the coordinated iron; neither are they observed as contact or pseudocontact shifted resonances. The NMR titration of the three free histidines establishes them as normal histidines with pK' values of 7.00 +/- 0.03 and Hill coefficients of 0.90, 0.81, and 0.81 +/- 0.03. The chemical shift of the protonated and neutral histidines is normal, and the bandwidth of the resonance absorption is 5 Hz. A pH-dependent reversible transition in the chemical shift of the histidine C(2)H occurs at pH 6.5; above this pH the three protons occur as a singlet but break into three singlets of different chemical shift at acid pH values. Two of the three "free" histidines have been identified by their susceptibility to photooxidation as His-82 and His-34.

Determination of microscopic acid?base parameters from NMR?pH titrations

“…Since the aromatic 1 H resonances of His and Tyr are well separated from the complicated aliphatic multiplets, earlier NMR-pH titrations focused mainly on these residues [206,207,208]. In fact, before the age of 2D NMR spectroscopy, protonation constants and 1 H [208,209,210] and 13 C [211] protonation shifts were used for peak assignment purposes in peptides and proteins, for example, serine proteases [208], hemerythrin [207], ribonuclease A [117,209], myoglobins [211], and lysosime [212].…”

“…In fact, before the age of 2D NMR spectroscopy, protonation constants and 1 H [208,209,210] and 13 C [211] protonation shifts were used for peak assignment purposes in peptides and proteins, for example, serine proteases [208], hemerythrin [207], ribonuclease A [117,209], myoglobins [211], and lysosime [212]. At present, pulse sequences are optimized specifically to ease protonation constant determination of particular residues [213].…”

Cyclization of (1-methyl-5-hexenyl)sodium in ethers

“…Understandably, success will be improved if the electrophilic partner is relatively inert toward direct reaction with P at 0 °C for short time periods. (9) (a) Brace, N. O. J. Org. Chem.…”

“…Michael J. Maroney, Randall B. Lauffer,7 and Lawrence Que, Jr.* Department of Chemistry, University of Minnesota Minneapolis, Minnesota 55455 Donald M. Kurtz, Jr. Department of Chemistry, Iowa State University Ames, Iowa 50011Received July9, 1984 Hemerythrin (Hr), a respiratory protein isolated from a number…”