Phosphoglycolate synthesis by human erythrocyte pyruvate kinase

Area of Science:

• Biochemistry
• Human Red Blood Cell Metabolism
• Enzymology

Background:

• Human red blood cells contain R2-type pyruvate kinase, an enzyme primarily known for its role in glycolysis.
• Glycolate metabolism and the potential synthesis of phosphoglycolate in red cells are not fully understood.

Purpose of the Study:

• To investigate the glycolate kinase activity of purified R2-type pyruvate kinase from human red cells.
• To determine the physiological relevance of this enzymatic activity in vivo.

Main Methods:

• Monogeneous purification of R2-type pyruvate kinase from human red blood cells.
• Enzymatic assays to measure glycolate kinase activity under varying substrate and cofactor concentrations.
• Kinetic analysis including Km and activation parameters.
• Comparison of enzyme activity with physiological concentrations of metabolites.

Main Results:

• Purified R2-type pyruvate kinase exhibits glycolate kinase activity.
• Enzyme activity is modulated by fructose-1,6-bisphosphate and glucose-1,6-bisphosphate.
• Kinetic parameters (Km for glycolate and ATP) were determined.
• At physiological concentrations of substrates and activators, the enzyme's glycolate kinase activity is insufficient to account for reported phosphoglycolate levels.

Conclusions:

• The glycolate phosphorylation activity of R2-type pyruvate kinase in mature red cells is likely not physiologically significant.
• The source of phosphoglycolate in red cells remains uncertain, suggesting potential alternative pathways or questioning its presence.