Biochemical and surface characteristics of human tear proteins.

Pooled human tear samples were subjected to biochemical and surface chemical analyses. Gel filtration chromatography yielded four fractions. The second fraction was the most surface active, closely followed by the first. By ionic exchange chromatography, the first fraction obtained by gel filtration chromatography could be further separated into three subfractions. The second of these subfractions was found to be the most surface active, even surpassing the combined surface activity of all the tear components. Altogether eleven protein components were identified in human tears by gradient polyacrylamide gel electrophoresis with sodium dodecyl sulfate (SDS). Their molecular weights range from 16,000 to 400,000 daltons. Isoelectric focusing indicated that most of the tear proteins are negatively charged, whereas the rest are positively charged at physiological pH's.