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.
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 Mg(2+)-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 B(12) and total antioxidant status (TAS) were measured using commercial kits, Hcy was determined by HPLC and membrane enzyme activities were measured spectrophotometrically.


RESULTS
Mg(2+)-ATPase remained unaltered. Membrane Na(+),K(+)-ATPase activity was remarkably increased in patients (0.77+/-0.06 micromol Pi/h x mg protein) and decreased to normal levels (0.52+/-0.05 micromol Pi/h x 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 micromol/L) than levels after therapy (12.1+/-2.0 micromol/L; p<0.001) and in controls (10.5+/-2.5 micromol/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.
Schulpis
Kleopatra H
KH
1. Institute of Child Health, Research Centre, "Aghia Sophia" Children's Hospital, Athens, Greece.
Giannoulia-Karantana
Aglaia
A
Papaconstantinou
Evangelos D
ED
Parthimos
Theodore
T
Tjamouranis
Ioanna
I
Tsakiris
Stylianos
S
D000251:Adenosine Triphosphatases / Q000187:drug effects / Q000378:metabolism*; D000328:Adult; D000409:Alanine / Q000494:pharmacology; D000975:Antioxidants / Q000032:analysis; D016022:Case-Control Studies; D002474:Cell-Free System; D002478:Cells, Cultured; D004910:Erythrocyte Membrane / Q000201:enzymology*; D005838:Genotype; D006801:Humans; D020138:Hyperhomocysteinemia; D008297:Male; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics*; D010649:Phenylalanine / Q000494:pharmacology; D020641:Polymorphism, Single Nucleotide; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000378:metabolism*
D000975:Antioxidants; D010649:Phenylalanine; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D000251:Adenosine Triphosphatases; C035123:magnesium sodium ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D000409:Alanine