Genetic variation in the proteins of human nail.

In a survey of the proteins from human nail, genetic variation has been observed in both the low-sulfur and high-sulfur protein fractions. The low-sulfur proteins were examined by polyacrylamide gel electrophoresis at pH 7 in the presence of sodium dodecyl sulfate, whilst the high-sulfur proteins were characterized by gel electrophoresis at pH 2.6 in 3 M urea. Of 106 samples of apparently normal nail, 69% showed a characteristic pattern of 3 major low-sulfur and 5 major high-sulfur proteins. The remaining samples showed an additional high-sulfur band, and about half of these samples also manifested an additional major low-sulfur band. The proportion of nail samples containing the variant proteins was much higher in some families. Two-dimensional eletrophoresis of the low-sulfur proteins showed five major low-sulfur components in the normal nail with an additional component in the variant sample. Peptide maps of the proteins showed that the additional protein was sufficiently different in amino acid sequence to the other proteins to indicate that a mutation in a structural gene had not occurred. In the high-sulfur protein fractions, over 30 proteins were observed in the two-dimensional electrophoretic patterns and there were at least 3 additional components in the variant fraction.