Haptoglobin. Haptoglobin, an α 2 glycoprotein, is synthesized in the hepatocytes and, to a small extent, in cells of the reticuloendothelial system. Haptoglobin comprises two kinds of polypeptide chains: two α chains and one β chain. There are three possible α chains and only one form of β chain. On starch-gel electrophoresis, haptoglobin exhibits three types of patterns, which illustrates the polymorphism in the a chains. Homozygous haptoglobin 1-1 gives 1 band. The peptide chains form polymers with each other and with haptoglobin 1 chains to provide the other two electrophoretic patterns, which have been designated as Hp 2-1 and Hp 2- 2 phenotypes.
Haptoglobin increases from a mean concentration of 0.02 g/L at birth to adult levels within the first year of life. As old age is approached, haptoglobin levels increase, with a more marked increase being seen in males. Radial immunodiffusion and immunonephelometric methods have been used for the quantitative determination of haptoglobin.
The function of haptoglobin is to bind free hemoglobin by its α chain. Abnormal hemoglobin, such as Bart's and hemoglobin H, has no α chains and cannot be bound. The reticuloendothelial cells remove the haptoglobin-hemoglobin complex from circulation within minutes of its formation. Thus, haptoglobin prevents the loss of hemoglobin and its constituent iron into the urine.
Ceruloplasmin. Ceruloplasmin is a copper-containing, α2-glycoprotein that has enzymatic activities (i.e., copper oxidase, histaminase, and ferrous oxidase). It is synthesized in the liver, where six to eight atoms of copper, half as cuprous (Cu+) and half as cupric (Cu2+) ions, are attached to an apo-ceruloplasmin. Ninety percent or more of total serum copper is found in ceruloplasmin.
α 2 M a c r o g l o b u l i n . α 2 - M a c r o g l o b u l i n , a d i m e r i c , l a r g e p r o t e i n , i s s y n t h e s i z e d b y h e p a t o c y t e Because its movement is restricted due to size, it is found principally in the intravascular spaces. However, much lower concentrations of α2 macroglobulin can be found in other body fluids, such as CSF On binding with and inhibiting proteases, it is removed by the reticuloendothelial tissues. s .