( Joseph W. Turek and Guy ...)Isolation of Low Molecular Weight Digestion Products of the Human Platelet Thromboxane A2 Receptor, Rev A

Joseph W. Turek and Guy C. Le Breton, Department of Pharmacology, University of Illinois at Chicago, College of Medicine, Chicago, IL 60612. Address correspondence to: Joseph W. Turek, 835 South Wolcott, Department of Pharmacology M/C 868, University of Illinois at Chicago, Chicago, IL 60612. E-mail: jturek1@icarus.uic.edu

Introduction
The human platelet thromboxane A₂ (TXA₂) receptor, in addition to its normal role in hemostasis, has been implicated in the pathogenesis of multiple cardiovascular diseases.¹ Studies suggests that increased platelet production of the natural ligand, TXA₂, may lead to enhanced platelet aggregatory activity, predisposing an individual to spontaneous platelet aggregation, followed by thrombus formation. Attempts to develop specific antagonists to block the TXA₂ receptor have been hampered by a lack of information concerning the receptor ligand-binding domain.

Labeling of receptors, followed by sequential receptor digestion, accumulation, and sequence identification of labeled fragments, has become a commonly used approach to identify receptor ligand-binding domains.²⁶ However, the initial digestion product contains a wide mixture of proteins, from smaller peptides which cannot be separated by traditional glycine gel electrophoresis, to larger proteins not effectively purified using reversed-phase or size exclusion HPLC. In addition, the limited availability of certain receptor proteins (including the TXA₂ receptor) has hindered the isolation of sufficient amounts of labeled fragments. To circumvent these problems, we have coupled continuous elution preparative gel electro
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