Mechanism of Histamine Binding I: Effect of Calcium on Binding of Histamine to a Plasma Peptide

Abstract

A method of isolating a single polypeptide from human plasma, termed peptide H for its histaminopexic or histamine-binding capability, is described. The peptide was obtained by acid precrystallization of human plasma, followed by water extraction of the precipitate and separation on an ion-exchange column. A molecular weight of 4492 was calculated from amino acid analysis. A dynamic dialysis technique was used to study the binding of histamine to peptide H. No binding of histamine to peptide H was observed in the absence of Ca+2; however, in the presence of Ca+2, binding of histamine to peptide H did occur. It was determined that histamine first forms a complex with Ca+2, with subsequent binding of the Ca+2-histamine complex to peptide H. From the dialysis data and kinetic analysis, it was possible to demonstrate that the data are consistent with a peptide having three binding sites for the Ca+2-histamine complex, two fast sites and one slow site.