ULTRACYTOCHEMISTRY OF THE CELL MEMBRANE I. THE DEMONSTRATION OF INTRAMEMBRANOUS AMINO GROUPS IN RABBIT ERYTHROCYTIC MEMBRANE BY THE HYDROQUINONE-TETRANITROBLUE TETRAZOLIUM SYSTEM

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Abstract
Amino groups in rabbit erythrocytic membranes were ultracytochemically demonstrated using the hydroquinone-tetranitroblue tetrazolium system. Reaction products were observed within the membrane, which was immediately external to the phosphotungstic acid-positive zone, in the form of small globules or particles with generally a diameter of 3.0-9.0 nm, aligning in 1 or several rows. By use of a goniometer stage, the membrane area with several rows of particles was found to correspond in reality to the tangentially cut area of that with 1 row of particles. The detected intramembranous amino groups seemed to have originated from proteins, probably globular proteins, rather than from carbohydrates or lipids, since reaction products detected were found within the membrane and resisted extraction of specimens in organic solvents as well as digestion by phospholipase C, but were not found in specimens treated with protease. These findings are of great interest in relation to intramembranous particles observed in freeze-fractured or freeze-etched membranes of various cells and also to the hypothesis of the fluid mosaic model of the cell membrane.

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