Comparative lipophilicities of substrates of monoamine oxidase.
Oil/water partition coefficients of various substrates of monoamine oxidase (MAO) and kinetic parameters of MAO-A and -B of rat liver at two pH values, pH 7 and pH 9, were investigated. Octanol, heptane or benzene were chosen for the oil phases. The deamination of the biogenic amines 5-hydroxytryptamine (5-HT), tyramine, 2-phenethylamine (PEA) and benzylamine was studied at pH 7 and pH 9. Results indicated all four substrates were very hydrophilic, and the oil/water partition coefficients of benzylamine and PEA were higher than those of 5-HT and tyramine. The changes in Km and Vmax values at pH 7 and pH 9 indicated that the affinities of MAO-A towards 5-HT and tyramine slightly increased at pH 9 and those of MAO-B towards tyramine and benzylamine also increased at pH 9, while uncharged amines at pH 9 amounted to about a hundred times of those at pH 7. It is concluded that the mitochondrial MAO bound to the membrane may metabolize charged molecules as well as uncharged counterparts.
Katayama
M
M
Yamamoto
M
M
Kobayashi
S
S
Oguchi
K
K
Yasuhara
H
H
D000818:Animals; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008055:Lipids / Q000032:analysis*; D008297:Male; D008930:Mitochondria, Liver / Q000201:enzymology; D008995:Monoamine Oxidase / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012995:Solubility; D013379:Substrate Specificity
D008055:Lipids; D008995:Monoamine Oxidase