Distribution and heterogeneity of histamine N-methyltransferase

Abstract

The distribution of histamine N-methyltransferase (HMT) was studied in several tissues of various animal species including mice, rat, guinea pig, rabbit, cat and dog. The highest activity of the enzyme was found in the cat kidney and cat intestine which was two-fold higher than that in guinea-pig brain. This is in sharp contrast to the findings of Brown et al. (1) who reported that guinea-pig brain had highest activity of this enzyme. The enzyme from the four best sources (cat kidney, cat intestine, guinea pig brain and rabbit intestine) was studied and shown to exist in multiple forms. It was concluded that there were at least three multiple forms of HMT in the four sources tested, whereas the homogeneity of the enzyme was found in the two tissues from cat. Further, there appeared to be no correlation between histamine content and HMT activity in at least eight different enzyme sources tested including cat brain, kidney and intestine, guinea pig brain and liver, rat intestine and kidney, and rabbit intestine. This suggests that HMT may not be the only enzyme responsible for histamine metabolism in these tissues. © 1972.