Lysozyme, carbon-13 spectrum

Using 20 mm tubes the sensitivity of natural abundance PFT 13C NMR can be increased drastically, as was demonstrated first for hen egg-white lysozyme. For example, the 13C NMR spectrum recorded under these conditions shows 22 signals for 28 non-protonated aromatic carbons, however, with a broad background arising from 59 proto-nated aromatic carbons [916]. 

Figure 25-29 shows an unusually well-resolved 13C nmr spectrum of the enzyme lysozyme (Table 25-3 and Figure 25-15) taken with proton decoupling. The closely spaced peaks on the left side of the spectrum are of the carbonyl groups. The peaks in the center are of unsaturated and aromatic carbons, while those on the right are of the aliphatic amino acid carbons. The five sharp resonances marked at about 110 ppm with arise from tryptophan carbons marked with in 22 ... 

Figure 25-29 Carbon-13 nmr spectrum at 45.3 MHz of lysozyme, 0.015M in water solution, taken with proton decoupling (Section 9-10L)...

Proton resonance spectra of denatured proteins consist of sharp peaks which correspond to a summation of resonances from individual residues [129]. In C spectra of denatured proteins, it is possible to distinguish all the carbon resonances of the aromatic side chains of histidine, phenylalanine, tyrosine and tryptophan, and separate resonances from alanine, arginine, glycine, isoleucine, leucine, threonine, valine and occasionally methionine [130]. (A natural abundance C spectrum of a 13 mM solution of lysozyme takes only 4 hr accumulation time using 20 mm sample tubes [131]). 

Lysozyme contains six tryptophan residues whose gamma-carbon resonances have been identified in the 107 to 115 ppm region of the 30 °C spectrum and partially assigned by Allerhand et al. [2]. 

Fig. 6. Proton decoupled C-13 NMR spectrum of the alpha carbons region of lysozyme at different temperatures. 20000 transients were collected and Fourier transformed after performing a negative exponential multiplication (TC=—5) to enhance sensitivity. Computer resolution 3 Hz.

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