MINERAL METABOLISM 387 



with amounts disastrous for cattle. Areas toxic ior cattle contain 

 0.002 per cent mol) btlenum or more in the surface soils, }jroviding like 

 concentrations (on a dry basis) in the forage from these fields. Plants 

 with 0.0005 per cent (5 p. p.m.) molybdenum are harmless, but when 

 the element is deliberately increased to the toxic range, the usual symp- 

 toms are observed. In cattle the symptoms include severe diarrhea, 

 marked weight loss, disturbance of phosphate metabolism, reproduc- 

 tive impairment and failure, and bone and joint abnormalities. 



Several aspects of molybdenum poisoning resemble the symptoms of 

 copper deficiency. When this similarity was realized, it was discovered 

 that feeding extra Cu++ prevents the symptoms of molybdenum 

 toxicity. Thus an excess of molybdenum is antagonistic for copper 

 and raises the requirement for the latter. In addition, experiments 

 have shown that feetling sodium sulfate accelerates the excretion of 

 molybdenum and raises the level which may be ingested safely. Similar 

 results have been obtained in rats, where both copper and methionine 

 are beneficial in alleviating the toxicity. Clearly, then, molybdenum 

 poisoning depends upon the dietary levels of three elements, molybde- 

 num, copper, and sulfiu. 



Phosphate 



Phosphorus as organic and inorganic phosphates is, next to calcium, 

 the most abundant "mineral" element in the animal. Of that present, 

 70 to 80 per cent is associated with Ca++ in bones and teeth, llie 

 remainder is dispersed throughout the soft tissues as organic esters like 

 ATP, DPN + , glucose-1 -phosphate, phosphoproteins, phospholipides, 

 nucleic acids, and inorganic phosphate. The roles of the phosphoryl- 

 ated metabolic intermediates are discussed in Chapter 9 on metab- 

 olism and Chapter 7 on energy. Some phosphoproteins are enzymes 

 like pepsin, while others have different roles like casein, which in part 

 supplies needed phosphorus to young animals. Phosphorus is struc- 

 turally essential in nucleic acids and phospholipides. The roles of 

 these compounds are discussed in other chapters. Inorganic phosphate 

 is one of the reactants in many metabolic reactions and is formed in 

 still others. None of the other elements discussed in this chapter plays 

 such numerous and diverse roles as phosphate. 



Human beings should receive approximately as much phosphorus 

 as calcium with about 1 g. daily for adults and growing children. 

 Slight increases are desirable during adolescence, the period of maxi- 

 mum growth. During the latter part of pregnancy 1.5 g. daily is rec- 

 ommended to meet the demands of the fetus, and 2.0 g./day is needed 

 in lactation to provide replacement for that in milk. Seeds, legumes. 



