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Haptoglobins and hemoglobin-haptoglobin complexes

University of British Columbia

Haptoglobins are serum glycoproteins which form complexes with hemoglobin. Three phenotypes of haptoglobin exist in serum (Hp 1-1, Hp 2-1, Hp 2-2). The latter two types exist as a series of polymers while the former type exists as a homogeneous protein. All three haptoglobin types consist of β (heavy), chains and α (light) chains which are attached by disulphides. The haptoglobin types differ in their a chains; Hp 1-1 contains only α¹ chains, while Hp 2-2 contains only α² chains and Hp 2-1 contains α¹ and α² chains. The hemoglobin-haptoglobin 1-1 complex consists of one molecule of hemoglobin attached to one molecule of haptoglobin. The thesis has been divided into three parts. The first part (Section III) is concerned with the reaction of haptoglobin with an octameric (double) hemoglobin obtained from an inbred strain of mice. In this hemoglobin each of the hemoglobin dimers is joined together by a disulphide bond. The fact that haptoglobin binds αβ dimers indicates that it is a bivalent molecule like the antibody molecule, immunoglobulin G (IgG). This bivalence and resultant resemblance to IgG is examined by studying the reaction of haptoglobin with this mouse hemoglobin in which the αβ dimer is held together by a disulphide bond. The results of both precipitation studies and acrylamide gel electrophoresis confirm the postulated bivalence of haptoglobin and its resemblance to an antibody. The second part (Section IV) of the thesis is concerned with confirming the results obtained in studying the disulphides of haptoglobin which were obtained by the cysteic acid diagonal technique. These results predicted a model in which the two halves of the haptoglobin molecule were held together by a disulphide bond at position 21α. Also the results predicted an intrachain loop disulphide between half-cystines at positions 35 and 69 in the haptoglobin α chain and an interchain disulphide between a half-cystine at position 73α and the β chain. This structure has been confirmed by studies on a cyanogen bromide fragment isolated from haptoglobin which contains the intact a chain. Also the structure has been confirmed by studies on a haptoglobin derivative in which the molecule has been split in half by the breaking of a disulphide bond. The third part (Section V) of this thesis is an investigation into the nature of the β93 sulphydryl of hemoglobin when hemoglobin is bound by haptoglobin. The results demonstrate that there is a definite change in the environment of this sulphydryl upon formation of the hemoglobin-haptoglobin complex. Studies with (14)C-iodoacetamide demonstrate however that β93 can still react in the HbHp complex.

Text

2011-06-09

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http://hdl.handle.net/2429/35361

Biochemistry and Molecular Biology

University of British Columbia

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