Zinc is an important metallic constituent of the enzyme carboxypeptidase A, a pancreatic enzyme active in protein degradation. Zinc is found in highest concentration in the liver, with lesser amounts found in the pancreas, kidney, and pituitary gland. Zinc absorption occurs primarily in the small intestine. Zinc-binding ligand molecules act to transport zinc across the mucosal cells of the intestine, where it is picked up by albumin molecules for transport to the liver and other organs. Zinc is a constituent of the enzyme carbonic anhydrase. This enzyme is, in turn, a constituent of red blood cells and gastric juices, and plays an important role in the deposition of calcium salts in teeth and bones. The enzyme alcohol dehydrogenase contains zinc and is essential for the conversion of alcohol to an aldehyde, thereby facilitating alcohol metabolism in the liver. The function of this enzyme and its relationship to the development of liver cirrhosis is conspicuously tied to characteristic zinc deficiencies in alcoholic patients. Zinc is found in other enzymes as well, including lactic dehydrogenase (active in glycolysis), alkaline phosphatase (active in maintaining phosphate levels near bone), and glutamic dehydrogenase (found in blood platelets). Zinc is important as a structural constituent for RNA proteins and is essential for the proper activity of the RNA synthesizing enzyme RNA polymerase. Zinc also plays a role in metabolism and three dimensional structure of DNA. Zinc is found in alpha-macroglobulin, an important protein in the body’s immune system. This globulin firmly binds about 30% of plasma albumin, which functions primarily as a transport protein. Zinc appears to be a cofactor in the synthesis and degradation of collagen, and has effects in reproduction and healing. Factors which can impair zinc absorption include calcium, fiber, copper, iron, and various diseases, such as Crohn’s disease.