Guinea Pig Brain Histamine N‐Methyltransferase: Purification and Partial Characterization

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Abstract
Histamine N-methyltransferase (EC 2.1.1.8) was purified 4400-fold in 12% yield from guinea pig brain. The basic steps in the purification included differential centrifugation, calcium phosphate adsorption, DEAE-cellulose chromatography and affinity chromatography on an S-adenosylhomocysteine-agarose matrix. The resulting protein was shown to be homogeneous by gel electrophoresis and was stable for at least 3 mo. at -80.degree. C. It had an apparent MW of 29,000 .+-. 1000 as determined by both gel filtration through Sephadex G-100 and by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. The isoelectric point of the protein was 5.3. The pH optima for methylation of histamine were 7.5 and 9.0; the Km for histamine and S-adenosyl-L-methionine were 13.57 .+-. 0.74 .mu.M and 6.1 .+-. 0.12 .mu.M, respectively; the Ki for S-adenosyl-L-homocysteine was 24.5 .+-. 1.45 .mu.M.