[Presence of a PCR-inhibitor in hairs]

A polymerase chain reaction (PCR) system was used to amplify the noncoding 333-bp region of mitochondrial DNA (mt333DNA) contained in DNA extracts from single human hairs, and the following results were obtained: 1) Using natural black hairs, mt333 DNA was always amplified from a 5-cm length of hair shaft sampled within a region 11 cm from the hair root, but it was not always amplified from a 5-cm region adjacent to this 11-cm region, and was not amplified in almost all cases when a 5-cm length of hair shaft was sampled from a region more than 16 cm distant from the hair root. DNA preparations not responding to PCR were colored dark brown. 2) Using natural white hairs, mt333DNA was amplified from almost all specimens even up to a length of 31 cm. 3) When natural black hairs were stained with an oxidation-type hair-staining agent (Bigen-5Ge), mt333DNA was never amplified even from the hair root portion, whereas the same staining treatment of white hairs did not influence the amplification of mt333DNA. In the cases showing no response on PCR, DNA preparations were also colored dark brown. 4) These dark brown DNA preparations inhibited completely the amplification of mt333DNA even after addition of purified DNAs. These results suggest that the dark brown substance in the DNA preparations inhibits the amplification of mt333DNA by the PCR method. We therefore investigated the mechanism responsible for the development of this inhibitor. It was found that hydrogen peroxide (a component of hair-staining agent) induced formation of water-soluble melanins from insoluble melanins.(ABSTRACT TRUNCATED AT 250 WORDS)