A novel mutation of human liver alanine:glyoxylate aminotransferase causes primary hyperoxaluria type 1: immunohistochemical quantification and subcellular distribution.

[primary hyperoxaluria type 1]

A novel alanine :glyoxylate aminotransferase (AGT ) mutation involved in primary hyperoxaluria type 1 (PH 1 ) was studied in Japanese patients . Two mutations in exon 7 , c .751 T >A and c .752 G >A , lead to a W 251 K amino acid substitution . Proband 1 (patient 1 ) was homozygous for the W 251 K mutation allele (DDBJ Accession No . AB 292648 ), and AGT -specific activity in the patient 's liver was very low . To reveal the cause of the low enzymatic activity , the intracellular localization of AGT (W 251 K ) was studied using immunohistochemistry and immunoelectron microscopy . The latter analysis showed that patient 2 had only one -fifth of the normal AGT expression per catalase , suggesting impairment of AGT (W 251 K ) dependent transport into peroxisomes . Peroxisomal transport of human AGT is believed to be dependent on the presence of the type 1 peroxisomal targeting sequence . The C-terminal tripeptide of AGT , KKL is necessary for peroxisomal targeting . In cultured cells , EGFP-AGT (W 251 K ) localized both in the peroxisome and cytosol . These results were consistent with the data obtained from liver analysis of patient 2 . The subcellular distribution of AGT (W 251 K ) and the results from a random mutagenesis study suggest that KKL is necessary for peroxisomal targeting of human AGT , but additional signal other than KKL may be necessary .