S-adenosylhomocysteine (SAH) is a crucial biochemical compound formed from the demethylation of S-adenosylmethionine (SAM), serving as a key intermediate in the methylation cycle. It plays a significant role in regulating cellular methylation processes and is subsequently hydrolyzed to homocysteine and adenosine, which can be recycled back into SAM, highlighting its importance in maintaining cellular homeostasis.