Some properties of the low molecular weight α-crystallin from normal human lens: Comparison with bovine lens

Abstract

Low molecular weight α-crystallin (6 × 10 5−9 × 10 5 daltons) was isolated from normal human lenses of various ages and from bovine lenses by gel filtration on Sephadex G-100 followed by chromatography on an Agarose A-15 m-column. The elution pattern obtained from the Agarose column for the human and bovine lenses was identical. A value of 2·5 × 10 −7 cm 2/sec at 22°C for the translational diffusion coefficient was observed for both the human and the bovine fractions using laser light seattering experiments. Similar far ultraviolet circular dichroism (CD) spectra were obtained from human and bovine lenses. The near ultraviolet spectrum of α-crystallin shows a complex wavelength profile (vibronic structure) between 240 and 300 nm. These vibronic transitions arise from tryptophan, tyrosine and phenylalanine residues. The α-crystallin wavelength profiles from bovine and normal human lenses of various ages were the same. Dissociating the low molecular weight α-crystallin subunits with guanidine-HCl greatly altered the near ultraviolet spectrum, indicating conformational changes. Removal of the guanidine-HCl yielded a far ultraviolet spectrum indistinguishable from that of native α-crystallin. On the other hand, the native near ultraviolet spectrum could not be regenerated upon removal of the guanidine-HCl. No conformational changes were observed upon addition or removal of calcium ions. From the similarity in the elution patterns, translational diffusion coefficient, and near ultraviolet CD wavelength profiles of the bovine and the human low molecular weight α-crystallin, it can be concluded that, in spite of some differences in amino acid composition, both fractions possess similar secondary and tertiary structures.