Abnormal thiol reactivity of tropomyosin in essential hypertension and itsassociation with abnormal sodium-lithium countertransport kinetics

Objectives To identify a thiol protein that is abnormal in a subgroup of es sential hypertensive (EHT) patients who have a strong family history of hyp ertension and cardiovascular disease and have a low Km of erythrocyte Na/Li countertransport(CT) Methods To detect biotin maleimide labelling of a key thiol protein to inve stigate its reaction with N-ethylmaleimide (NEM) in normal and EHT erythroc ytes, Results The thiol protein of 33 kDa apparent molecular weight (p33) identif ied by the loss of labelling with biotin maleimide was identified as tropom yosin due to its retarded running in 6 mol/l urea gels and immunoblotting, The NEM reaction with p33 detected by loss of subsequent biotin maleimide l abelling is biphasic in normal control erythrocytes with the rate in the fi rst 30 s double that after 30 s. In EHT erythrocytes NEM reaction (1)after 30 s is faster than normal and (2) in the first 30 s causes a paradoxical i ncrease in apparent biotin maleimide labelling. In normal control erythrocy tes, the loss of biotin maleimide labelling with NEM reaction or the faster phenylmaleimide reaction follows the same time course as the decrease in K m of Na/Li CT. Conclusions NEM reaction with p33 requires two thiols. Only the cytoskeleta l form of tropomyosin from the TM3 gene has more than one thiol group and a grees with SDS-PAGE mobility, Tropomyosin is a strong candidate to explain the familial abnormality in EHT with abnormal Na/Li CT and it could explain many of the characteristics of this disease. I Hypertens 19:485-493 (C) 20 01 Lippincott Williams & Wilkins.