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S-adenosylhomocysteine hydrolase from rat liver
Canadian Journal of Biochemistry
|February 1, 1982
Summary
This study determined kinetic constants for rat liver adenosylhomocysteine hydrolase. The enzyme exhibits specific Michaelis constants (Km) and maximum velocities (Vmax) for its synthetic and hydrolytic reactions.
Area of Science:
- Biochemistry
- Enzymology
Background:
- Adenosylhomocysteine hydrolase (AHH) plays a crucial role in regulating cellular S-adenosylhomocysteine (SAH) levels.
- Understanding AHH kinetics is vital for comprehending purine and methionine metabolism.
Purpose of the Study:
- To determine the kinetic constants for the reversible adenosylhomocysteine hydrolase from rat liver.
- To elucidate the enzyme's kinetic behavior in both synthetic and hydrolytic reactions.
Main Methods:
- Enzyme kinetics assays were performed using S-adenosylhomocysteine, adenosine, and L-homocysteine as substrates.
- Michaelis constants (Km) and maximum velocities (Vmax) were calculated for both forward and reverse reactions.
- Inhibition patterns were analyzed using L-homocysteine and adenosine.
Main Results:
- Km values for S-adenosylhomocysteine, adenosine, and L-homocysteine were determined to be 12.3 µM, 0.94 µM, and 164 µM, respectively.
- Vmax for the synthetic reaction was 6.2 µmol/min/mg, and for the hydrolytic reaction was 0.72 µmol/min/mg.
- Adenosine competitively inhibited both reactions (Ki = 1.2 ± 0.2 µM) and was identified as a reaction product.
Conclusions:
- The kinetic parameters provide a quantitative understanding of rat liver AHH activity.
- Adenosine's dual role as a substrate/product and inhibitor highlights its complex interaction with AHH.
- These findings contribute to the understanding of metabolic pathways involving AHH.