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Concomitance of an active and an inactive mutant of red cell pyruvate kinase (PK)
Abstract:
A new mutant red cell PK associated with mild chronic haemolytic anaemia is described. The propositus, double heterozygous for a maternal gene coding for a structural abnormal enzyme and a paternal gene coding for a catalitically inactive enzyme, was suitable for an accurate functional characterization of the PK variant since his erythrocytes contained only one active mutant form of this enzyme. The active isoenzyme was characterized by low activity, decreased affinity for phosphoenolpyruvate, incomplete fructose-1,6-diphosphate activation, increased 'zero-time transition temperature', increased stability to guanidine-HCl and storage at +4 degrees C, increased guanosine-5'-diphosphate and cytidine-5'-diphosphate utilization, altered electrophoretic pattern with a single slow-moving component and abnormal isoelectric point. Affinity for ADP, ATP inhibition, optimum pH, molecular weight of the subunits, antigen concentration and immunological properties were in the normal range.
Insights
A novel red blood cell pyruvate kinase (PK) variant linked to mild hemolytic anemia was identified. This PK variant exhibits reduced activity and altered kinetic properties, offering insights into enzyme function.
Area of Science:
- Biochemistry
- Hematology
- Genetics
Background:
- Pyruvate kinase (PK) deficiency is a known cause of hereditary hemolytic anemia.
- Characterizing novel PK variants is crucial for understanding red blood cell metabolism and disease pathogenesis.
Observation:
- A propositus with mild chronic hemolytic anemia was found to be double heterozygous for two PK gene mutations.
- This genetic makeup resulted in erythrocytes expressing only one active, abnormal PK isoenzyme, facilitating its study.
Findings:
- The characterized PK variant displayed significantly reduced enzymatic activity and decreased affinity for phosphoenolpyruvate.
- Further abnormalities included incomplete activation by fructose-1,6-diphosphate, altered thermal stability, and modified substrate utilization (GDP, CDP).
- Electrophoretic and isoelectric focusing revealed a distinct abnormal pattern, though some properties like ADP affinity and ATP inhibition remained normal.
Implications:
- This study provides a detailed functional characterization of a novel PK variant.
- Understanding the specific defects of this variant contributes to the broader knowledge of PK deficiency and its clinical spectrum.
- The findings may inform future diagnostic approaches and therapeutic strategies for related hemolytic anemias.