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Clinical Chemistry and Laboratory Medicine (CCLM)

Published in Association with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)

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Erythrocyte membrane Na+,K+-ATPase and Mg2+-ATPase activities in subjects with methylenetetrahydrofolate reductase (MTHFR) 677 C→T genotype and moderate hyperhomocysteinaemia. The role of L-phenylalanine and L-alanine

Kleopatra H. Schulpis1 / Aglaia Giannoulia-Karantana2 / Evangelos D. Papaconstantinou3 / Theodore Parthimos4 / Ioanna Tjamouranis5 / Stylianos Tsakiris6

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Corresponding author: Stylianos Tsakiris, PhD, Associate Professor, Department of Experimental Physiology, Medical School, University of Athens, P.O. Box 65257, 15401 Athens, Greece

Citation Information: Clinical Chemical Laboratory Medicine. Volume 44, Issue 4, Pages 423–427, ISSN (Online) 1437-4331, ISSN (Print) 1434-6621, DOI: 10.1515/CCLM.2006.069, April 2006

Publication History

Received:
October 25, 2005
Accepted:
January 3, 2006
Published Online:
2006-04-07

Abstract

Background: Increased homocysteine (Hcy) blood levels are correlated with vascular and neurological problems. The aim of our study was to investigate erythrocyte membrane Na+,K+-ATPase and Mg2+-ATPase activities in patients with methylenetetrahydrofolate reductase (MTHFR) 677 C→T genotype.

Methods: Blood was obtained from 25 patients before and after folic acid supplementation and from controls (n=30) once. Plasma folate, vitamin B12 and total antioxidant status (TAS) were measured using commercial kits, Hcy was determined by HPLC and membrane enzyme activities were measured spectrophotometrically.

Results: Mg2+-ATPase remained unaltered. Membrane Na+,K+-ATPase activity was remarkably increased in patients (0.77±0.06 μmol Pi/h × mg protein) and decreased to normal levels (0.52±0.05 μmol Pi/h × mg protein; p<0.001) after therapy. TAS did not differ significantly before and after treatment. Hcy levels were significantly higher before therapy (25.4±2.8 μmol/L) than levels after therapy (12.1±2.0 μmol/L; p<0.001) and in controls (10.5±2.5 μmol/L, p<0.001). In vitro, L-phenylalanine (Phe) reversed to normal the stimulated enzyme from patients before therapy. In addition, Phe incubation of the Hcy activated membrane Na+,K+-ATPase from controls resulted in restoration of its activity, whereas L-alanine (Ala) incubation protected the enzyme from Hcy activation.

Conclusions: The increased membrane Na+,K+-ATPase activity may be due to high -SH group Hcy levels. In vitro, Phe reversed the increase in enzyme activity induced by Hcy in controls, as well as the stimulated membrane enzyme in untreated patients. Ala protected the enzyme from Hcy action.

Keywords: L-alanine; erythrocyte membrane; hyperhomocysteinaemia; Na+,K+-ATPase; L-phenylalanine

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