THE MOLECULAR MECHANISM OF THE NEUTRAL-TO-BASE TRANSITION OF HUMAN-SERUM ALBUMIN - ACID-BASE TITRATION AND PROTON NUCLEAR MAGNETIC-RESONANCE STUDIES ON A LARGE PEPTIC AND A LARGE TRYPTIC FRAGMENT OF ALBUMIN

  • 15 January 1989
    • journal article
    • research article
    • Vol. 264  (2) , 953-959
Abstract
In order to obtain a better understanding of the neutral-to-base (N-B) transition of human serum albumin, we performed acid/base titration experiments and 500-MHz 1H NMR experiments on albumin and on a large peptic (residues 1-387) and large tryptic (residues 198-585) fragment of albumin. The acid/base titration experiments revealed that Ca2+ ions induce a downward pK shift of several histidine residues of the peptic (P46) fragment and of albumin. By contrast, Ca2+ has very little influence on the pK of histidine residues of the tryptic (T45) fragment. In albumin, the pH-dependent His C-2 proton resonances, observed with 1H NMR experiments, have been allotted the numbers 1-17. It proved possible to locate these resonances in the P46 and the T45 fragments. A correspondence was found between the number of histidines detected by the acid/base titration and by the 1H NMR experiments. The results of the experiments lead us to conclude that in domain 1 at least the histidines corresponding to the His C-2 proton resonances 1-5 play a dominant role in the N-B transition. The Cu2+-binding histidine residue 3 (resonance 8) of the albumin molecule is not involved in the N-B transition. In addition, we were able to assign His C-2 proton resonance 9 to histidine 464 of the albumin molecule. The role of the N-B transition in the transport and cellular uptake mechanism of endogenous and exogenous compounds is discussed.

This publication has 22 references indexed in Scilit: