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Sorghum prolamins: their optical rotatory dispersion, circular dichroism, and infrared spectra

Wu, Y.V., Cluskey, J.E., Jones, R.W.
Journal of agricultural and food chemistry 1971 v.19 no.6 pp. 1139
Sorghum bicolor, grain sorghum, prolamins, protein conformation, infrared spectroscopy, optical properties, circular dichroism spectroscopy, solvents, protein secondary structure
The molecular conformation of sorghum prolamin was explored because of its high levels of nonpolar amino acids, its strong tendency to gel, and its poor solubility. Conformations of prolamin from 4 hybrids of grain sorghum were studied by optical rotatory dispersion (ORD), circular dichroism (CD), and IR spectra in several solvents. IR absorption spectrum of prolamin in 60% tert-butyl alcohol (tert-BuOH) and D2O showed the presence of α-helix and unordered structure, as well as the absence of β-structure. ORD data of the prolamins in 60% tert-BuOH give α-helix content of 40-47% independent of hybrids and of colour of the prolamin solution. The α-helix content of the prolamins in 60% tert-BuOH + 1.5M guanidine hydrochloride (G-HCl) is lowered somewhat to 34-40%, but is greatly reduced in 6M G-HCl. The CD and far UV ORD curves of decolorized prolamin give α-helix content in agreement with that from ORD data. The high level of α-helix for sorghum prolamin supports the concept that H bonds between backbone polypeptide chains are protected from aqueous or other polar residues by a nonpolar environment resulting from the side chains.