AN IMPROVED MODIFICATION OF PERMANGANATE OXIDATION OF EUMELANIN THAT GIVES A CONSTANT YIELD OF PYRROLE-2,3,5-TRICARBOXYLIC ACID

Microanalysis of eumelanin is based on the formation of pyrrole-2,3,5- tricarboxylic acid (PTCA) on permanganate oxidation followed by its HP LC determination. A problem in this method was that the oxidation gave concave, exponential curves when the amounts of PTCA formed were plot ted against the amounts of sample oxidized. The problem has been mostl y overcome by adding a homogenate of 5 mg of a mouse liver to the oxid ation medium. Sepia melanin, C57BL black mouse hair, B16 mouse melanom a, and MM418 human melanoma cells were oxidized in the absence or pres ence of the liver homogenate. The yields of PTCA increased about 1.5-f old by adding the liver homogenate and the calibration curves became l inear or almost linear. With the improved method the PTCA values from various types of samples can be reliably compared.