The Incorporation of Labeled Amino Acids into Lens Protein

¹ Howe Laboratory of Ophthalmology, Harvard Medical School, and the Massachusetts Eye and Ear Infirmary, Boston, Mass.

Calf and rabbit lenses cultured in a medium containing a radioactive amino acid incorporate some labeled amino acids into a minor protein fraction, the HL (high labeled) protein, three or four times more rapidly than into any other soluble lens protein. This fraction, isolated by DEAE chromatography, represents about 11 per cent of the total protein but contains about 34 per cent of the total radioactivity. High rates of incorporation into this protein fraction were obtained with C-14 arginine, histidine, and aspartic acid--the three amino acids studied. The rapidly synthesized HL component is clearly not associated-with the gamma-crystallin group, but, since it is not yet pure, it cannot be related, to either the alpha or beta crystallin fractions at the present time. The specific activity of the protein in the equatorial and anterior regions teas found to be much greater than that of the protein in the remainder of the lens. The core incorporated little C-14 amino acid although the concentration of labeled amino acid in this section was 65 per cent as high as that in the equatorial region. However, all lens sections examined gave the same over-all pattern of incorporation into the different protein fractions.