Search PubMed⌕ Search

Biomedical subjects

H L Van Camp

Publications and source records attributed to H L Van Camp.

5 recordsLinked to original sources
PubMed1984

Electron paramagnetic resonance- (EPR-) resolved kinetics of cryogenic nitric oxide recombination to cytochrome c oxidase and myoglobin.

By the electron paramagnetic resonance (EPR) technique, recovery kinetics for nitric oxide (NO) to heme following cryogenic photolysis were studied for the nitrosylferrocytochrome a3 center in cytochrome c oxidase and for myoglobin. The recovery was nonexponential, as has been observed in previous cryogenic CO and O2 rebinding to heme systems. NO rebinding to heme a3 started near a temperature of 50 K and was related to a distribution of thermal activation energies. At the peak of the distribution the activation energy was 3.1 kcal/mol, and the preexponential in the recovery rate was 10(9.9) s-1. For recovery of NO back to the a3 heme, the activation energy was threefold less than that for CO where CO binds to nearby Cua3 following photolysis from heme a3, but was larger than the activation energy for CO, O2, and probably NO rebinding to myoglobin. NO ligand rebinding to myoglobin occurred at a temperature as low as 15 K and in a temperature regime where tunneling could occur. However, the rate of NO rebinding to myoglobin did increase with temperature in the 15-25 K range.

Animals↗
PubMed1982

An examination of the cyanide derivative of bovine superoxide dismutase with electron-nuclear double resonance.

The Cu(II) sites of native, azido- and cyano-derivatives of bovine superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1) have been examined by electron-nuclear double resonance (ENDOR). The ENDOR spectrum of the native protein taken at the g parallel extreme shows resolved structure due to the directly coordinated N-atoms of the histidine ligands. These spectra are too complex for interpretation but suggest inequivalent coupling between the electronic spin and the four ligand N-atoms. By contrast, the azido protein reveals one type of nitrogen with well-resolved hyperfine and quadrupole splittings (Azz = 37.9 +/- 1 MHz, Pzz = 1.54 +/- 0.02 MHz), and the cyano from reveals one well-resolved set of nitrogen lines (Azz = 47.8 +/- 0.4 MHz, Pzz = 1.62 +/- 0.01 MHz) and one type of partially resolved nitrogen (Azz = 37.0 +/- 1 MHz). The cyano form also reveals a complex spectrum in the low-frequency domain (1-10 MHz). Through isotopic substitution and computer stimulation, the spectrum is shown to be a composite of the ENDOR from the remote imidazole nitrogens and the cyanide nitrogen. The component of the hyperfine constant perpendicular to the C14N bonds axis is A perpendicular N = 3.9 +/- 0.3 MHz and along the bond axis is A perpendicular N approximately equal to 5.7 MHz. The quadrupole interaction appears to be greatest along the CN axis with Qz'z' = 1.0 +/- 0.1 MHz and Qx'x'y'y' approximately 0. Based on an analysis of the hyperfine and quadrupole interactions seen at two extremes of the electron paramagnetic spectrum, we propose a square-planar arrangement of three imidazole nitrogen and one CN- carbon around the copper. Within this plane two imidazole nitrogens are strongly coupled and magnetically equivalent, the third is inequivalent (slightly weaker hyperfine interactions) and forms a trans relationship with the cyanide. This model is consistent with other observations on the cyano-derivative.

Animals↗
PubMed1976

ENDOR from nitrogens and protons in low spin ferric heme and hemoprotein.

Electron nuclear double resonance (ENDOR) signals have been obtained from iron-linked nitrogens in frozen solutions of cytochrome c, metmyoglobin cyanide, and a low spin protohemin mercaptide complex. Hyperfine couplings from heme protons have also been obtained from metmyoglobin cyanide and from a low spin protohemin cyanide complex. Several of these proton resonances are assigned to specific heme protons.

Binding Sites↗
PubMedDate not supplied

An equivalent squares template.

A template for calculating equivalent squares of irregularly shaped fields is described. Calculations using the template are essentially scatter summations. Comparisons with a computer program showed good agreement in equivalent squares and tumor doses (within 0.8%). Comparisons with area-perimeter ratio methods of computing equivalent squares showed consistently better accuracy using the template. For highly irregular fields, the template calculation required 3-10 min for central axis computation, comparable to that required by the other manual methods.

Humans↗