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Decreased Na,K-ATPase activity by glycation at the catalytic center
T Katori1, C Bannai, Y Hayashi
1Division of Endocrinology and Metabolism, Institute of Clinical Medicine, University of Tsukuba, Ibaraki, Japan.
Abstract:
The in vitro activity of Na,K-ATPase isolated from outer medulla of dog kidney was decreased in a dose- and time-dependent manner by interaction with 100 mM glucose 6-phosphate (G6P) during the first 8 h. In the subsequent 16 h no change in activity was observed. On the other hand, Amadori-products of the enzyme increased in a dose- and time-dependent manner by glycation up to 100 mM G6P during 24 h. The presence of 5 mM ATP in glycation experiments protected the enzyme activity but did not inhibit the formation of Amadori-products. These results were consistent with inhibition of the Na,K-ATPase activity by glycation of the amino groups located in the catalytic center of the molecule.
Insights
Glucose 6-phosphate (G6P) exposure decreases dog kidney Na,K-ATPase activity and increases enzyme glycation. ATP partially protects activity but not glycation, suggesting G6P inhibits Na,K-ATPase by modifying amino groups.
Area of Science:
- Biochemistry
- Renal Physiology
- Enzymology
Background:
- Na,K-ATPase is crucial for maintaining ion gradients in kidney tubules.
- Glycation, a non-enzymatic modification of proteins, can alter enzyme function.
- The impact of glucose 6-phosphate (G6P) on Na,K-ATPase activity requires further elucidation.
Purpose of the Study:
- To investigate the in vitro effects of G6P on Na,K-ATPase activity and glycation.
- To determine the role of ATP in mitigating G6P-induced changes in Na,K-ATPase.
- To explore the mechanism by which G6P affects Na,K-ATPase function.
Main Methods:
- Isolation of Na,K-ATPase from dog kidney outer medulla.
- Incubation of the enzyme with varying concentrations of G6P over time.
- Measurement of enzyme activity and Amadori-product formation.
- Assessment of ATP's protective effects on enzyme activity and glycation.
Main Results:
- G6P decreased Na,K-ATPase activity in a dose- and time-dependent manner within the first 8 hours.
- Amadori-product formation, indicative of glycation, increased with G6P exposure over 24 hours.
- ATP (5 mM) protected enzyme activity but did not prevent glycation.
Conclusions:
- G6P inhibits Na,K-ATPase activity through glycation of amino groups in the catalytic center.
- ATP can partially preserve Na,K-ATPase function under glycation conditions.
- These findings highlight a potential mechanism for impaired renal function in conditions with elevated G6P.