Simplified enzymatic synthesis and biodistribution of ¹¹C-S-adenosyl-l-methionine

¹¹C-S-Adenosyl-l-methionine (¹¹C-SAM) was synthesized enzymatically from ¹¹C-l-methionine using ratliver extract [40%-50% saturated (NH₄)₂SO₄ fraction] as the enzyme source. In biodistribution studies in rats, the highest uptake of ¹¹C-SAM was found in the kidneys. ¹¹C-SAM was also accumulated in the small intestine, pancreas, adrenal gland, liver, and spleen. The uptake of ¹¹C-SAM in the brain increased with time, but remained low. At 30 min after injection, about 50%-60% of the ¹¹C radioactivity was present in the acid-insoluble fraction of the kidneys and liver. When a high loading dose of ¹¹C-SAM was administered, the kidney uptake was enhanced, but the proportion of the radioactivity present in the acid-insoluble fraction was lower. In a study of one rabbit, the kidney uptake was of ¹¹-SAM clearly visualized using positronemission tomography.