THE LOCALIZATION AND SIGNIFICANCE OF ARGININE AND CITRULLINE IN PROTEINS OF THE HAIR FOLLICLE

Abstract

The Sakaguchi reaction for arginine and the Ehrlich reagent for citrulline, which was modified to lessen tissue swelling, have been used to localize these amino acids in the inner sheath and the medulla layers in sections of actively growing hair follicles of the rat. The trichohyalin droplets are rich in arginine but gave no detectable reaction for citrulline. Conversely, the hardened substance of the inner sheath and of the medulla gave a relatively weak reaction for arginine but an intense one for citrulline. The presence of high concentrations of citrulline in the proteins of the hardened inner sheath and medulla has only recently been reported from chemical studies. The results support biochemical and electron microscope studies indicating a conversion of arginine residues into citrulline residues without protein breakdown, concomitant with the morphological transformation of trichohyalin droplets into the hardened fibrous protein of the inner sheath or the hardened amorphous material of the medulla. Other possible biochemical functions for the inner sheath and the medulla are also discussed.