Abstract:
:We have investigated in detail the cooperativity which we had previously observed in the pH titration profiles of the histidine residues of rabbit tropomyosin [Edwards, B. F. P., & Sykes, B. D. (1978) Biochemistry 17, 684]. Nonpolymerizing tropomyosin was prepared by carboxypeptidase digestion, and the titration profiles of its histidine residues were compared with those of undigested tropomyosin which was fully polymerized (in 0.1 M KCl) throughout the titration. We have concluded that both histidine-153 and histidine-273 have significant cooperativity in their pH titrations only in polymerized tropomyosin, that the cooperativity arises from an intrinsic pH-dependent conformational transition which links the two residues together and not from the known pH dependence of the polymerization, and that the best model for the cooperativity is a biallosteric adaption of the Monod--Wyman--Changeux formalism involving two classes of binding sites for the same ligand (protons). Three other models which postulated either a Hill transition, an interaction with a neighboring residue that also titrates, or a pH-dependent polymerization were also considered.
journal_name
Biochemistryjournal_title
Biochemistryauthors
Edwards BF,Sykes BDdoi
10.1021/bi00517a037subject
Has Abstractpub_date
1981-07-07 00:00:00pages
4193-8issue
14eissn
0006-2960issn
1520-4995journal_volume
20pub_type
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