BIOCHEMICALLY IMPORTANT MINERAL ELEMENTS 



187 



copper protein, hemocuprein, which has been purified and obtained in 

 the form of blue crystals containing 0.34 per cent of copper. The copper 

 in hemocuprein and in a similar substance, called hepatocuprein, in the 

 liver accounts for nearly all the copper in the bodies of higher animals and, 

 presumably, also in human beings. 



The function of iron in the body is to serve as one of the essential raw 

 materials for the various physiologically important iron-containing sub- 

 stances listed above. Given an adequate dietary supply of iron, the 

 body can synthesize whatever amounts of hemoglobin and the iron- 

 porphyrin enzymes it may need, provided, however, that sufficient amounts 

 of copper are also supplied by the food intake. Just how copper func- 

 tions in this regard is not understood, but it is an observed fact that 

 copper is needed for the proper absorption and utilization of iron. It 

 is not surprising, therefore, that diets low in either copper or iron lead 

 to the development of nutritional anemia, that is, an abnormally low 

 amount of hemoglobin in the blood, which is corrected by consuming a 

 complete diet. An average family diet contains about 2 mg. of copper 

 per person per day. 



The tissues of the body are dependent almost entirely upon hemo- 

 globin for their oxygen supply. In the lungs, where relatively large 

 amounts of oxygen are available from the inhaled air, hemoglobin is 

 converted into oxyhemoglobin. The oxygen is held in a rather loose 

 combination and is easily given off' whenever the oxyhemoglobin reaches 

 a place w4iere the prevailing oxygen pressure is low, that is, where 

 little oxygen is present. This occurs normally, of course, in the muscles. 



Hemoglobin also functions indirectly in the transportation of carbon 

 dioxide to the lungs. Oxyhemoglobin is a stronger acid than hemoglobin 

 itself and when it is formed in the lungs combines with a certain amount 

 of potassium. As the oxyhemoglobin changes to hemoglobin in the 

 muscles, this potassium is released and combines with carbon dioxide to 

 form potassium bicarbonate. This substance is then carried back to 

 the lungs where the potassium is taken up by freshly produced oxyhemo- 

 globin, and the bicarbonate radical becomes free carbonic acid. The last 

 step in the process of eliminating carbon dioxide involves the decomposi- 

 tion of this newly formed carbonic acid. Here still another mineral 

 element, namely zinc, plays an essential role, since it is a component of 

 carbonic anhijdrase, an enzyme, present in red blood cells, which greatly 

 speeds up the breakdown of carbonic acid: 



carbonic 



H2CO3 < * H2O + CO2 



anhydrase 



As a result of the action of this enzyme, carbon dioxide is released in 

 gaseous form and exhaled as rapidly as it is brought to the lungs. 



The iron-containing enzymes, such as cytochrome, are very widely 



