Abstract
Natural abundance 13C Fourier transform NMR spectra (at 15.18 MHz, in 20-mm sample tubes) of aqueous native proteins yield numerous narrow single carbon resonances of nonprotonated aromatic carbons. Techniques for the assignment of these resonances are presented. Each technique is applied to one or more of the following proteins: ferricytochrome c from horse heart and Candida krusei, ferrocytochrome c and cyanoferricytochrome c from horse heart, lysozyme from hen egg white, cyanoferrimyoglobins from horse and sperm whale skeletal muscle, and carbon monoxide myoglobin from horse. In all of the protein spectra we have examined, methine aromatic carbons give rise to broad bands. Studies of the narrow resonances of nonprotonated aromatic carbons of proteins are facilitated by removal of these broad bands by means of the convolution-difference method, preferably from spectra recorded under conditions of noise-modulated off-resonance proton decoupling. We present a summary of the chemical shift ranges for the various types of nonprotonated aromatic carbons of amino acid residues and hemes of diamagnetic proteins, based on our results for hen egg white lysozyme, horse heart ferrocytochrome c, horse carbon monoxide myoglobin, and carbon monoxide hemoglobins from various species...
Highlights
From the Department of Chemistry, Indiana University, Bloomington, Natural abundance 13C Fourier transform NMR spectra of aqueous native proteins yield numerous narrow single carbon resonances of nonprotonated aromatic carbons
Studies of the narrow resonances of nonprotonated aromatic carbons of proteins are facilitated by removal of these broad bands by means of the convolution-difference method, preferably from spectra recorded under conditions of noise-modulated off-resonance proton decoupling
We present a summary of the chemical shift ranges for the various types of nonprotonated aromatic carbons of amino acid resiuues and hemes of diamagnetic proteins, based on our results for hen egg white lysozyme, horse heart ferrocytochrome c, horse carbon monoxide myoglobin, and carbon monoxide hemoglobins from various species
Summary
Horse heart cytochrome c was purchased from Sigma Chemical Co., St. Louis, MO. (type III and VI) and from Calbiochem, La Jolla, Calif. (A grade). Noise-modulated off-resonance proton-decoupling experiments have shown that all of the narrow resonances in the aromatic region of the 13C NMR spectra of all of the native proteins that we have examined [1,2,3, 5, 6] arise from nonprotonated carbons. Shift ranges for the various types of nonprotonated aromatic carbons of diamagnetic proteins, based on our assignments for hen egg white lysozyme, horse heart ferrocytochrome c, carbon monoxide myoglobins (see below), and carbon monoxide hemoglobins [6].
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