The pH-dependence of the equilibrium between the fast- and slow-folding forms of bovine prothrombin fragment 1: a role for pH-induced self-association?
Examination of the pH- and ionic strength (mu)-dependence of the equilibrium between fast- and slow-folding forms of bovine prothrombin fragment 1 reveals a sharp dependence of Keq ([% fast-folding form]/[% slow-folding form]) and % fluorescence quenching (%Q) on pH at low mu, and the absence of a pH-dependence of Keq at high mu (0.1 M NaCl) and much reduced pH-dependence of %Q, suggesting that the ionization process is coupled to other processes, such as self-association. The observed low mu pH effect on Keq amounts to a 10% increase in the % of the fast-folding form of prothrombin at low pH. We hypothesize the existence of a pH-dependent self-association of bovine prothrombin fragment 1. This process is associated with a conformation change involving an ionizing group with pKa in the neighborhood of 6.5 and a change in Keq from 0.27 to 0.45.
Malhotra
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OP
Medical Research Service, Department of Veterans Affairs, Cleveland, Ohio.
Chang
H Y
HY
Koehler
K A
KA
D000818:Animals; D002021:Buffers; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism*; D017510:Protein Folding; D011498:Protein Precursors / Q000737:chemistry* / Q000378:metabolism*; D011516:Prothrombin / Q000737:chemistry* / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D002021:Buffers; D010446:Peptide Fragments; D011498:Protein Precursors; C029733:prothrombin fragment 1; D011516:Prothrombin