A mutation of the methionine coding start codon (ATG) for S-COMT to threonine (ACC), corresponding to 'ATG' position +30 in exon2 of Comt gene and a floxed neo cassette in intron 4 were introduced by homologous recombination. The selection cassette was removed by cre mediated recombination. The S-COMT (24 kDa) isoform was absent on western blots of liver extracts, while the MB-COMT was detected. (J:164057)