BLOOD AND BLOOD DERIVATIVES — COHN 415 



Proteins are among the largest known molecules. All living tissue 

 contains proteins and the complexity of the protein molecule is such 

 that its synthesis in the laboratory is not yet envisioned. However, 

 it is synthesized in processes of biological growth, and the shape 

 and functions of the tissues may be thought of as depending in large 

 part upon the shape and structure of the proteins of which they are 

 composed. 



The protein within the red cells, which gives blood its color and per- 

 forms its prime respiratory function, is hemoglobin. Proteins are 

 largely composed of nitrogen, carbon, hydrogen, and oxygen organ- 

 ized in the more than 20 different amino acids which are the building 

 blocks of proteins. Hemoglobin contains hundreds of amino acids 

 held together by chemical combination, with loss of water, of the 

 amino and carboxyl groups which all possess. The synthesis of pro- 

 tein in the body is balanced by hydrolysis of these same links which 

 thus confer lability as well as specificity of structure upon these vast 

 protein molecules. 



Hemoglobin performs its specific respiratory function by virtue of 

 a relatively small prosthetic group, attached to the molecule but 

 readily separated from it, which is not composed of amino acids but 

 of iron in a configuration of pyrrole rings. The iron in this configura- 

 tion has a high avidity for oxygen, combines with it, and is the means 

 of its transport. The prosthetic group containing the iron is called 

 heme, the protein part of the molecule globin. 



Let us examine the relative masses of the oxygen needed by the 

 tissues and the various component parts of the mechanism which the 

 body employs for its transport. The atomic weight of oxygen is 16 

 and of iron 55. Each iron atom combines with an oxygen molecule, 

 that is, 2 oxygen atoms. The iron, however, is part of the heme group 

 with a combining weight close to 700. The heme is attached to the 

 globin, each iron to a unit of 16,700 equivalent weight. Iron-contain- 

 ing proteins concerned with respiration in muscle, known as myo- 

 globin, are of this size, but the hemoglobin of the blood stream has 

 a molecular weight of at least 33,400 and generally of 66,800, in the 

 former state combining and transporting 2, in the latter 4, oxygen 

 molecules. The molecule devised by nature for the efficient transport 

 of oxygen to the tissues thus has a mass roughly 500 times that of the 

 oxygen molecule to be transported. 



Why is the hemoglobin of the blood stream contained within cell 

 walls? The proteins which perform comparable respiratory func- 

 tions in many forms of life are free in the fluid part of the blood. 

 The proteins dissolved in the fluid part of the blood of animals rarely 

 exceed 10 percent, those dissolved in the fluid or plasma part of the 

 blood of man, 7 percent. This figure may be contrasted with the 30 



