Protein with a molecular weight of 100,000 shows a single boundary when centrifuged in aqueous buffer. Of the protein is centrifuged in a medium of the same buffer plus 6 M urea, two boundaries are observed, one corresponding to a molecular weight of 10,000, the other to a molecular weight of 30,000. The area of the slower peak is two-thirds that of the faster. Describe the subunit structure of the protein.