Abstract
The highly labeled (HL) protein fraction of calf lens has been purified and characterized. The purified protein has a specific activity eight to ten times greater than any other isolated lens protein fraction. Amino acid analyses and immunochemical experiments indicate that it is essentially identical to alpha crystallin. A study of the effect of temperature upon the SH reactivity to para-hydroxymercuribenzoate reveals an identical profile for the HL protein and the α1,-protein. However, there are a number of differences between the two proteins. Ultracentrifuge experiments demonstrate that the HL protein in contrast to alpha crystallin appears to be physically homogeneousin both the aggregated and deaggregated state. The aggregate molecule has an apparent molecular weight of (6.8 ± 0.2) x 105 and the sub-units an apparent molecular weight of (18.0 ± 0.2) x 103. Independent determinations of the Z average molecular weight give slightly higher values. Based on the summation of the weights of the amino acid residues in a subunit, a molecular weight of 20.0 x 103 has been calculated. The ninhydrin color yield per unit protein is 40 per cent greater with the HL protein than with alpha crystallin. Differences in electrophoretic mobility were also observed. The relationship between the HL protein and alpha crystallin and the basis for the observed differences between these proteins is discussed.