PT  - JOURNAL ARTICLE
AU  - AARBAKKE, JARLE
AU  - UELAND, PER M.
TI  - Interaction of <em>S</em>-Adenosylhomocysteine with Isolated Rat Hepatocytes
DP  - 1981 May 01
TA  - Molecular Pharmacology
PG  - 463--469
VI  - 19
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/19/3/463.short
4100  - http://molpharm.aspetjournals.org/content/19/3/463.full
SO  - Mol Pharmacol1981 May 01; 19
AB  - The time course of the association of radioactivity with isolated hepatocytes incubated in the presence of S-[14C]adenosylhomocysteine was characterized by an initial burst phase lasting for less than 15 sec (Phase I) followed by a slow linear phase (Phase II). Phase I was due to association of S-[14C]adenosylhomocysteine with the hepatocytes. The possibiity of intracellular resynthesis of S-[14C]adenosylhomocysteine from [14C]adenosine was ruled out. The process showed slight temperature dependence, and there was no effect of 2,4-dinitrophenol. These data argue against the possibility that Phase I was related to active uptake of S-[14C]adenosylhomocysteine, but rather suggest binding of this compound to an acceptor on the cell surface. Competition studies showed that S-adenosylhomocysteine was the preferred ligand of this acceptor. Phase II corresponded to intracellular accumulation of 14C-labeled adenine nucleotides and was nearly completely abolished by inhibitors of enzymatic hydrolysis of S-adenosylhomocysteine, such as adenosine and homocysteine. This process was explained by extracellular hydrolysis of S-[14C]adenosylhomocysteine catalyzed by S-adenosylhomocysteine hydrolase leaking out of the cells, followed by rapid uptake of [14C]adenosine. Trapping of adenosine formed from S-adenosylhomocysteine directed the extracellular enzyme catalysis towards hydrolysis. Extracellular hydrolysis of S-adenosylhomocysteine was the rate-limiting step in this sequence of events. It is concluded that S-adenosylhomocysteine was not taken up by rat hepatocytes as an intact molecule. ACKNOWLEDGMENTS The authors wish to thank Hallvard Bergesen and Audun Høylandskær for excellent technical assistance.