Lecture 6 — 143 — Biochemical Problems 



acts as an inhibitor in the organic acid respiration 

 chain presumably because its constitution permits it 

 to compete for sensitive groups in a protein enzyme, 

 but without power to act as a hydrogen acceptor or 

 donator. Malonic acid was observed to have an in- 

 hibiting effect on bromide accumulation which could 

 be neutralized, at least partially, by supplying suffi- 

 ciently large concentrations of one of the organic acids 

 of the respiration cycle. Another type of respiratory 

 inhibitor which can prevent ion accumulation is cya- 

 nide. It may be hoped that systematic studies on in- 

 hibitors will throw some light on the nature of respira- 

 tory systems that must operate to maintain the kind 

 of cell metabolism essential to ion accumulation. 



While the postulation may be made of the operation 

 of one of the organic acid cycles, from indirect evi- 

 dence, analysis of the roots discloses that malic acid 

 forms by far the larger part of the acid present. A 

 trace of oxalic and a small percentage of citric acid 

 are also found. Most of the total acid is thus ac- 

 counted for, by Isaacs, sometimes well over 90%, but 

 this fact would not preclude the presence of other 

 organic acids, formed in a cyclical process, effective 

 catalytically, but too small in amount to give a signifi- 

 cant value by the analytical methods utilized. 



Ion Accumulation and Protein Metabolism: — 



Steward and his collaborators have repeatedly 

 stressed, especially on the basis of experiments on 

 potato storage tissues, that the accumulation of salt 

 is dependent on metabolic processes intimately asso- 

 ciated with cell growth and protein synthesis. During 

 the process of salt absorption, when this brings about 

 an increase in content of both cations and anions in 

 the tissue, as occurs when potassium and bromide ions 

 are actively accumulated, certain soluble nitrogen com- 

 pounds are utilized in the building up of proteins. The 

 view is held that this protein metabolism, if it does 

 not have a direct part in the mechanism of salt ac- 



