Аннотация:Low-molecular keratin-associated proteins (KAPs) in human-hairshaft are considered as an important component capable of interactionwith structural water-insoluble keratin and with externalfactors (moisture, chemicals, UV light). Photo modification ofKAPs can be detected using thiol content as was shown earlier[Fedorkova M. et al 2016]. In the current study we comparedtotal amount of KAPs (as soluble proteins (SP, ug/mg) and thiolgroup (SH) content in these proteins (ug/mg) in grey and pigmentedhair shafts of 15 volunteers aged 45–70 years, withouthair coloring. A part of hair shafts in each sample were irradiatedwith UV-C light at an intensity of 1.5 mW/cm2 on the sampleusing the band of a mercury lamp peaked at 254 nm withrejection of remaining bands. Irradiated and control sampleswere homogenized and both SP and SH were assayed in theresulting supernatants. No significant difference was foundbetween pigmented and grey hairs in control samples. After UVirradiation SP increased by 16% in pigmented hairs (P < 0.05)and by 37% in grey hairs (P < 0.01), and SH content increasedby 44% and by 52%, respectively (P < 0.01). Thus, SP content inirradiated grey hair (221 46 ug/mg) was higher than that inpigmented hair (179 39 lg/mg), P < 0.05. The probable mechanismmay involve photoinduced damage of S-S bonds in insolublekeratins and/or between these keratins and KAPs withrelease of soluble peptides and proteins. Obviously, a pigmentedhair is protected with melanin unlike a grey one, which mayexplain difference in SP content after irradiation. It was alsofound that proximal segments of grey hairs (3–20 mm from hairbulb) were more sensitive to UV light than the distal (100–120mm from the bulb) ones: an increase in SP and SH content by81 and 57%, respectively, was obtained for the former, and anincrease in SP and SH content by 46 and 34%, respectively, wasobtained for the latter. *The authors marked with an asteriskequally contributed to the work.