title: Metal ion induced conformational transitions of prothrombin and prothrombin fragment 1.
abstract: Circular dichroism experiments indicate that prothrombin fragment 1 undergoes essentially the same secondary structural change whether in the presence of Ca(2+), Mg(2+), or Mn(2+). Titration with any of these metal ions results in a sigmoidal titration curve indicative of cooperative binding. Mg(2+) and Ca(2+) have nearly identical transition midpoints, while that for Mn(2+) is an order of magnitude less. These results correlate well with the results of previous metal ion intrinsic fluorescence quenching experiments. Fragment 1 has previously been shown to undergo a second transition corresponding to dimerization at high calcium concentrations. The present circular dichroism experiments show that this transition does not result in a gross alteration of secondary structure in the fragment 1 molecule. Studies with prothrombin, similar to those with fragment 1, indicate a similar metal ion dependent conformational change but of smaller magnitude. As apparently only the fragment 1 portion of the molecule undergoes the transition, it would appear that the covalently linked fragment 1 is constrained from attaining the same conformation as the purified entity. This suggests that caution must be used in interpreting the results of metal ion binding studies using fragment 1 as an analogue for prothrombin.
mesh_terms: D000818:Animals; D002118:Calcium; D002417:Cattle; D002942:Circular Dichroism; D006801:Humans; D008274:Magnesium; D008345:Manganese; D010446:Peptide Fragments; D011487:Protein Conformation; D011516:Prothrombin; D013056:Spectrophotometry, Ultraviolet
chemical_list: D010446:Peptide Fragments; D008345:Manganese; D011516:Prothrombin; D008274:Magnesium; D002118:Calcium