Erythrocyte membrane thiol proteins associated with changes in the kinetics of Na/Li countertransport: a possible molecular explanation of changes in disease.
BACKGROUND
Abnormal erythrocyte Na/Li countertransport is associated with diseases such as essential hypertension and diabetic renal disease. Although it seems unlikely that Na/Li countertransport contributes to any disease process, it may be abnormal because of a change in the cell membrane that is part of the disease process.


METHODS
We have shown that Na/Li countertransport kinetics are modified by two types of thiol group. One of these, which we have called 'type 1', is rapidly alkylated by N-ethylmaleimide to give a kinetic pattern similar to that in the above diseases.


RESULTS
AtpH 6 and 2 degrees C, both N-ethylmaleimide and iodoacetamide cause the K(m) of Na/Li countertransport to decrease to completion in 300s, with 78% (SEM 6%) of the decrease occurring in 30s. Using these reaction conditions, N-ethylmaleimide reacted with a unique thiol group on a 33-kD protein, blocking its subsequent reaction with biotin maleimide. This 33-kD protein was present in rabbit erythrocytes, which have high levels of Na/Li countertransport, but absent from rat erythrocytes, which have no Na/Li countertransport. Iodoacetyl biotin labelled a 60-kD protein that was specifically blocked by iodoacetamide.


CONCLUSIONS
We suggest that these proteins are members of a cluster of membrane proteins that can modify Na/Li countertransport and may have a functional role in the disease processes.
Thomas
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TH
Department of Medicine, University of Newcastle-upon-Tyne, UK. T.H.Thomas@ncl.ac.uk
Rutherford
P A
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Vareesangthip
K
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Wilkinson
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West
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IC
D000328:Adult; D000478:Alkylation; D000818:Animals; D017920:Antiporters / Q000097:blood*; D001710:Biotin; D003928:Diabetic Nephropathies / Q000097:blood*; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D006801:Humans; D006973:Hypertension / Q000097:blood*; D007700:Kinetics; D008094:Lithium / Q000097:blood*; D008297:Male; D008565:Membrane Proteins / Q000097:blood / Q000302:isolation & purification; D008875:Middle Aged; D011817:Rabbits; D051381:Rats; D012964:Sodium / Q000097:blood*; D013438:Sulfhydryl Compounds / Q000097:blood
D017920:Antiporters; D008565:Membrane Proteins; D013438:Sulfhydryl Compounds; C045885:sodium-lithium countertransporter; D001710:Biotin; D008094:Lithium; D012964:Sodium; D005033:Ethylmaleimide