A comparative study of methionine adenosyltransferase activity and regional distribution in mammalian spinal cord

To provide a background for future studies on neurodegenerative changes in the spinal cord, the present study analysed the distribution of the activity of methionine adenosyltransferase (ATP:L-methionine S-adenosyltransferase, EC 2.5.1.6, MAT), an enzyme that catalyses the synthesis of the biological methyl group donor S-adenosylmethionine (AdoMet), in spinal cords from bovine and pig, and compared the results with those from human spinal cord. The enzyme activity was estimated by a radiochemical method measuring the rate of formation of [(3)H]AdoMet from L-[methyl-(3)H]methionine and ATP. The MAT activity (V(max)) was quite homogeneously distributed between spinal regions and species investigated (19-50 pmol [(3)H]AdoMet/mg protein/minute), with the highest level found in the male bovine group. The bovine group (both males and females) also presented a 20% higher enzymatic activity in the dorsal horn as compared to the ventral horn and white matter areas. In the pig spinal cord, the highest level of activity was found in the white matter. The lowest affinity for methionine (highest K(m)) was found in the human spinal cord. Whole spinal cords of one cat and one rhesus monkey were also analysed and the levels of MAT activity were similar to that of humans and bovine females, respectively. Studies of MAT stability in the rat spinal cord (post-mortem time 0-72 hr) showed a significant decrease in enzyme activity during the interval of 0-8 hr (23 degrees ). From this time point on and up to 72 hr (4 degrees ), the significant decrease in the activity remained at 60% of the initial value.