Glycolate kinase activity in human red cells.

Area of Science:

• Biochemistry
• Human Physiology
• Enzymology

Background:

• Human red blood cells possess glycolate kinase activity.
• This activity is associated with pyruvate kinase and is reduced in individuals with hereditary pyruvate kinase deficiency.

Purpose of the Study:

• To characterize the glycolate kinase activity in human red cells.
• To determine the kinetic properties and physiological relevance of this enzyme activity.

Main Methods:

• Enzyme assays were performed to measure glycolate kinase activity.
• Kinetic parameters such as Km and Vmax were determined under various conditions.
• Activity was measured in the presence of fructose-1,6-diphosphate (FDP) or glucose-1,6-bisphosphate (G16P2).

Main Results:

• Glycolate kinase activity was detected and copurified with pyruvate kinase.
• The enzyme exhibited a low Km for adenosine triphosphate (ATP) (0.28 mmol/L) and a half-maximum velocity for glycolate at 40 mmol/L in the presence of FDP.
• The optimal pH for the reaction was above 10.5, and the calculated activity was very low (0.0013 U/mL RBC) under physiological conditions.

Conclusions:

• The measured glycolate kinase activity in human red cells is significantly low.
• This low activity suggests that the glycolate kinase reaction cannot account for the maintenance of phosphoglycolate levels in red blood cells.