Tyrosine uptake in normal and albino hairbulbs

A method for measuring tyrosine uptake by human hairbulbs was developed to further characterize the process of melanin formation in human tissue. Uptake was determined by incubating fresh anagen hairbulbs in 14C-tyrosine in HEPES-Tris buffer containing cycloheximide and catalase. Uptake for 11 normally pigmented subjects with brown, black, blond and red hair ranged from 295 cpm/24 h per hairbulb for hairbulbs from a blond subject to 6661 cpm/24 h per hairbulb for hairbulbs from a red-haired subject. Hairbulbs from a type IIA (tyrosinase-positive) oculocutaneous albino had an uptake of 2995 cpm/24 h per hairbulb. White hairbulbs had an uptake of 265 cpm/24 h per hairbulb. There was a good correlation (r = 0.86) between the level of uptake and the level of tyrosinase (tyrosine hydroxylase) activity when these values were compared for ten subjects. Uptake was reduced with the inhibition of tyrosinase activity. Uptake was also reduced with low incubation temperatures (4 degrees and 21 degrees C) and with the addition of unlabeled tyrosine to the incubation. From 14% to 19% of the 14C-tyrosine that was taken up could be extracted as 14C-melanin. These results show that the uptake of tyrosine as determined by this experimental method is dependent on the presence of melanocytes and tyrosinase, is quantitatively related to the level of tyrosinase activity, and appears to be a metabolic process. Type IIA albino hairbulb melanocytes appear able to transport adequate amounts of substrate.