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Erythrocyte membrane thiol proteins associated with changes in the kinetics of Na/Li countertransport: a possible molecular explanation of changes in disease
Author(s) -
Thomas Trian,
Rutherford Pa,
Kriengsak Vareesangthip,
Robert W. Wilkinson,
West Ic
Publication year - 1998
Publication title -
european journal of clinical investigation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.164
H-Index - 107
eISSN - 1365-2362
pISSN - 0014-2972
DOI - 10.1046/j.1365-2362.1998.00276.x
Subject(s) - iodoacetamide , thiol , chemistry , maleimide , kinetics , biochemistry , membrane , membrane protein , biophysics , endocrinology , medicine , cysteine , biology , enzyme , physics , quantum mechanics , polymer chemistry
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 At pH 6 and 2 °C, both N ‐ethylmaleimide and iodoacetamide cause the K m of Na/Li countertransport to decrease to completion in 300 s, with 78% (SEM 6%) of the decrease occurring in 30 s. 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. Conclusion 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.