Myocardial S-adenosylhomocysteine hydrolase is important for adenosine production during normoxia.

Abstract

The coronary vasodilator adenosine can be formed in the heart by breakdown of AMP or S-adenosylhomocysteine (SAdoHcy). The purpose of this study was to get insight into the relative importance of these routes of adenosine formation in both the normoxic and the ischemic heart. A novel HPLC method was used to determine myocardial adenosine and SAdoHcy. Accumulation of SAdoHcy was induced in isolated rat hearts by perfusion with L-homocysteine thiolactone or L-homocysteine. The release of adenosine, inosine, hypoxanthine, xanthine and uric acid was determined. Additional in vitro experiments were performed to determine the kinetic parameters of S-adenosylhomocysteine hydrolase. During normoxia the thiolactone caused a concentration-dependent increase in SAdoHcy. At 2000 microM of the thiolactone an SAdoHcy accumulation of 0.49 nmol/min per g wet weight was found during normoxia. L-Homocysteine (200 microM) caused an increase of 0.37 and 4.17 nmol SAdoHcy/min per g wet weight during normoxia and ischemia, respectively. The adenosine concentration in ischemic hearts was significantly lower when homocysteine was infused (6.2 vs. 11.5 nmol/g; P less than 0.05). Purine release was increased 4-fold during ischemia. The Km for hydrolysis of SAdoHcy was about 12 microM. At in vitro conditions favoring near-maximal SAdoHcy synthesis (72 microM adenosine, 1.8 mM homocysteine), the synthesis rate in homogenates was 10 nmol/min per g wet weight. From the combined in vitro and perfusion studies, we conclude that S-adenosylhomocysteine hydrolase can contribute significantly to adenosine production in normoxic rat heart, but not during ischemia.

• Authors: P W Achterberg, P P de Tombe, E Harmsen, J W de Jong
• Journal: Biochimica et biophysica acta (Biochim Biophys Acta) Vol. 840 Issue 3 Pg. 393-400 (Jul 05 1985) ISSN: 0006-3002 [Print] Netherlands
• PMID: 4005294 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Homocysteine
• homocysteine thiolactone
• Hydrolases
• Adenosylhomocysteinase
• Adenosine

Topics

• Adenosine (biosynthesis)
• Adenosylhomocysteinase
• Animals
• Coronary Disease (metabolism)
• Homocysteine (analogs & derivatives, metabolism)
• Hydrolases (metabolism)
• In Vitro Techniques
• Kinetics
• Male
• Myocardium (metabolism)
• Perfusion
• Rats
• Rats, Inbred Strains