Measurement of the formation of betaine aldehyde and betaine in rat liver mitochondria by a high pressure liquid chromatography-radioenzymatic assay.
A new assay procedure for measurement of rat liver mitochondrial choline dehydrogenase was developed. Oxidation of [methyl-14C]choline to [methyl-14C]betaine aldehyde and [methyl-14C]betaine was measured after isolating these compounds using HPLC. We observed that NAD+ was required for conversion of betaine aldehyde to betaine in rat liver mitochondria. In the absence of this cofactor, oxidation of choline led to the accumulation of betaine aldehyde. The apparent Km of the mitochondrial choline dehydrogenase for choline was 0.14-0.27 mM, which is significantly lower than previously reported. A partially purified preparation of choline dehydrogenase catalyzed betaine aldehyde formation only in the presence of exogenous electron acceptors (e.g., phenazine methosulfate). This preparation failed to catalyze the formation of betaine even in the presence of NAD+, indicating that betaine aldehyde dehydrogenase may be a separate enzyme from choline dehydrogenase.
Zhang
J
J
Department of Nutrition, School of Public Health, University of North Carolina, Chapel Hill 27599-7400.
Blusztajn
J K
JK
Zeisel
S H
SH
D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000818:Animals; D001622:Betaine / Q000031:analogs & derivatives* / Q000378:metabolism*; D002794:Choline / Q000378:metabolism*; D050545:Choline Dehydrogenase; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D066298:In Vitro Techniques; D008930:Mitochondria, Liver / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012995:Solubility
D001622:Betaine; C026820:betaine aldehyde; D000429:Alcohol Oxidoreductases; D050545:Choline Dehydrogenase; D002794:Choline