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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.