title: Noninvasive measurement of protein concentration.
abstract: At selected magnetic field strengths, protein and water proton spin-lattice relaxation rates are sensitive to the concentration of rotationally immobilized peptide nitrogen because of field dependent heteronuclear cross relaxation coupling between protein proton and nitrogen-14 spins that is carried to the water by proton homonuclear cross-relaxation. Measurement of the water proton spin-lattice relaxation time, or a signal amplitude proportional to it, may provide a noninvasive measure of peptide bond concentration, which provides a direct measure of immobilized protein content in most tissues. The approach using protein gels in two magnetic field strengths is demonstrated. At 66.7 mT; the proton Zeeman energy matches one of the peptide nitrogen transitions dominated by the unaveraged nuclear electric quadrupole interaction; cross-relaxation between the protons and nitrogen-14 is efficient. At 77.5 mT, the proton Zeeman energy is not matched with the nitrogen energy and proton-nitrogen cross-relaxation is not efficient. It is shown that the difference in the water proton spin-lattice relaxation rates on and off the energy level match condition is a linear function of the rotationally immobilized protein concentration.
authors.affiliation: Department of Chemistry, University of Virginia, Charlottesville 22901, USA.
authors.forename: X
authors.initials: X
authors.lastname: Jiao
authors.forename: R G
authors.initials: RG
authors.lastname: Bryant
mesh_terms: D000818:Animals; D066298:In Vitro Techniques; D009682:Magnetic Resonance Spectroscopy; D019047:Phantoms, Imaging; D011506:Proteins / Q000032:analysis*; D011522:Protons; D051381:Rats; D014867:Water
chemical_list: D011506:Proteins; D011522:Protons; D014867:Water