Rat histamine N-methyltransferase. Quantification, tissue distribution, purification, and immunologic properties.

Histamine N-methyltransferase is a major enzyme for inactivating histamine in mammalian tissues. Development of a sensitive and specific assay for histamine N-methyltransferase has permitted quantification of this activity in 25 rat tissues. Additionally, renal histamine N-methyltransferase was purified to electrophoretic homogeneity. The pivotal step in the purification scheme was an affinity column procedure which involved the specific elution of histamine N-methyltransferase from DEAE-Sephacel by 1 mM histamine. The purified enzyme has a molecular weight of 33,400 and a narrow pH dependency with an optimum at 8.0-8.25. Specific antibody produced to renal histamine N-methyltransferase also immunoprecipitated the brain enzyme completely, therefore indicating neuronal and non-neuronal histamine N-methyltransferase share common antigenic determinants.