Abstract
A nonradioactive, sensitive, rapid, and specific method for the determination of methionine adenosyltransferase activity has been established. In this method, the methyl group of S-adenosyl- l-methionine was enzymatically transferred to esculetin with the aid of catechol- O-methyltransferase and then the resulting scopoletin was extracted with n-hexane:ethyl acetate (7:3, v/v) and measured by high-performance liquid chromatography with Si 60 column and fluorometric detection with excitation and emission wavelengths at 347 and 415 nm, respectively. The detection limit for scopoletin was about 100 fmol. Using this method to determine MAT activity in HL-60 cells required only about 2.5 μg of protein and the incubation time needed for enzymatic reaction is less than 30 min. The HPLC analysis procedure took only 5 min per sample. The kinetic study showed that MAT in HL-60 cells exhibited negative cooperativity with a Hill coefficient of 0.5. The values of K m and V max were 6.1 ± 0.3 μM and 135.4 ± 1.5 nmol AdoMet formed/mg protein/h, respectively.
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