ATP-diphosphophydrolase activity in rat heart tissue

Area of Science:

• Biochemistry
• Cardiovascular Physiology
• Molecular Biology

Background:

• Extracellular nucleotides are crucial signaling molecules in the heart.
• These nucleotides are regulated by cell surface enzymes called ecto-nucleotidases.
• Understanding the specific enzymes involved is key to comprehending cardiac nucleotide metabolism.

Purpose of the Study:

• To biochemically characterize the ATPase and ADPase activities in rat heart sarcolemma.
• To determine if these activities belong to a single enzyme, ATP-diphosphohydrolase (apyrase).
• To elucidate the potential physiological role of this enzyme in cardiac interstitial nucleotide regulation.

Main Methods:

• Biochemical assays of ATPase and ADPase activities in isolated rat heart sarcolemma.
• Inhibition studies using mitochondrial ATPase and adenylate kinase blockers.
• Enzyme characterization including isoelectric focusing and electrophoresis under acidic conditions.
• Analysis of enzyme properties such as metal ion dependence, pH optimum, and substrate specificity.

Main Results:

• Both ATPase and ADPase activities were localized to the rat heart sarcolemma.
• These activities were demonstrated to be properties of a single enzyme, ATP-diphosphohydrolase (apyrase).
• The enzyme exhibited broad specificity for nucleoside di- and triphosphates and shared characteristics with 5'-nucleotidase.
• ATPase and ADPase activities could not be separated by isoelectric focusing or electrophoresis.

Conclusions:

• Rat heart sarcolemma possesses a single ATP-diphosphohydrolase (apyrase) enzyme with both ATPase and ADPase functions.
• This enzyme likely plays a significant role in hydrolyzing extracellular nucleotides in the cardiac interstitial space.
• Apyrase, in conjunction with 5'-nucleotidase, contributes to the regulation of nucleotide signaling in the heart.