Glyoxalase-I cDNA clones were isolated from a human colon cDNA library using polyclonal antibodies raised against the protein purified from human colon tissue. Positive clones were purified, subcloned, and their nucleotide sequence determined. The glyoxalase-I cDNA encodes a 184-amino acid protein with a predicted molecular weight of 20,774, corresponding to the monomeric subunit weight of the purified protein from human colon glyoxalase-I. The human enzyme showed 51% homology at the nucleotide level and 42% at the amino acid level with bacterial glyoxalase-I. Transfection of COS-1 cells with the 622-base pair cDNA containing the entire coding region cloned into a pMT2 vector produced an immunoreactive protein and an approximate 180-fold increase in glyoxalase-I enzyme activity as determined with methylglyoxal as a substrate. Transfection of a truncated cDNA lacking 94 base pairs of the 5'-coding sequence also produced an approximately 15-kDa immunoreactive protein, but with no detectable increase in enzyme activity. Northern analysis of the RNA showed an approximately 12-fold increase of the 2.2-kilobase glyoxalase-I transcript in carcinoma when compared to normal colon tissue from the same patient. Examination of colon carcinomas for the amplification of the glyoxalase-I gene by Southern blot analysis revealed no change in gene copy number. These results suggest induction of the glyoxalase-I gene expression in colon carcinomas.