BRAIN ATP-L-METHIONINE S-ADENOSYLTRANSFERASE (MAT), S-ADENOSYLMETHIONINE (SAM) AND S-ADENOSYLHOMOCYSTEINE (SAH) - REGIONAL DISTRIBUTION ANDAGE-RELATED-CHANGES

The distribution of the activity of the enzyme methionine adenosyltran sferase (ATP:L-methionine S-adenosyltransferase, EC 2.5.1.6, MAT) was investigated in human postmortem brains of individuals without a known history of neuropsychiatric disorders. The brain regions were the fro ntal, temporal, parietal and occipital cortices, nucleus caudatus, put amen, globus pallidus, thalamus and white matter. The activities in th e nucleus caudatus and putamen were approximately 25% higher than the activities in the seven other brain regions, however, not on a statist ically significant level. The apparent values of MAT K-m and V-max in the parietal cortex were 11.41+/-3.51 mu M methionine and 25.72+/-3.90 nmol/mg protein/h, respectively. In the frontal cortex, a significant positive correlation between age and the activity of MAT was found (r =0.997, P<0.01). Concerning MAT stability in the rat brain, there was a steady decrease in the activity with postmortem time in the brains k ept for 0-72 h at room temperature (23 degrees C), which reached the l evel of significance at 24 h. The activity did not change significantl y when the brains were kept for 120 h at 4 degrees C, or by freezing a nd thawing the tissue before analysis. In a parallel study in rats of different ages (2-22 months), a homogeneous distribution of SAM and SA H was observed in the cortex, striatum, midbrain, hypothalamus, brains tem and cerebellum. The lowest levels of SAM and the highest levels of SAH observed in the striatum gave the lowest SAM/SAH ratio. The SAH c ontent of rat cerebral cortex was highest in the oldest group. The lev els of S-adenosylmethionine (SAM) decreased by 38% and that of S-adeno sylhomocysteine (SAH) increased by 200% when the brains were kept for 2 h at 23 degrees C. In the brains kept for 24 h at 4 degrees C, the l evels of SAM decreased by 70% while those of SAH increased by 240%.