The Localization and Significance of Arginine and Citrulline in Proteins of the Hair

SUMMARY The Sakaguchi reaction for arginine and the Ehrlich reagent for citmulhine, which was modified to lessen tissue swelling, have been used to lo-cahize these amino acids in the inner sheath and the medulla layers in sections of actively growing hair follicles of the rat. The tnichohyahin 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 anginine but an intemmse one for cit rulhimie. The presence of high concentrations of citrulhine in the proteins of the hardened inner sheath and medulla has only recently been reporte(h from chemical studies. The results support biochemical and electron nuicroscope studies indicating a conversion of arginine residues into citrulline residues without protein breakdown, concomitant with the morphological transformmuation of trichohyalin droplets into the hardened fibrous protein of the inner sheath or the hardened amorphous material of time medulla. Other possible biochemical functions for the inner sheath and the medulla are also discussed.