Quarterly Journal of Microscopical Science, Vol s3-105, 113-122, Copyright © 1964 by Company of Biologists

The Union of Protein and Nucleic Acid in the Living Cell and its Demonstration by Osmium Staining

¹ A.R.C. Unit of Insect Physiology, Department of Zoology, Cambridge

The greater part of the osmium tetroxide that is reduced and bound by living cells in neutral solution is taken up by unsaturated lipids. The protein in mitochondria, muscle-fibres, connective tissue, red blood cells, &c, takes up a smaller amount of osmium; but the basic proteins that are combined with DNA and RNA in the chromosomes, nucleoli, and cytoplasm do not react: their reactive groups are presumably held in salt linkages with the phosphate residues of the nucleic acids.

If the cells are exposed to an acid medium (0.001 M acetic acid or saturated carbonic acid) these salt linkages are weakened, and chromosomes and cytoplasmic nucleoprotein will now take up large amounts of osmium and stain intensely with ethyl gallate. This effect of hydrogen ion concentration is reversible within the living cell.

By the application of a series of blocking reagents it is concluded that the chief reactive groups on the proteins are the guanidino group of arginine, the e-amino group of lysine, the iminazole group of histidine, and the pyrrolidine group of proline. Tryptophane and cystein, though highly reactive, are perhaps less important quantitatively.