Over street and Dean 95 



On the other hand, Brooks (8) became interested in the role of amino 

 acids in plant cells. He was led to the theory that the properties of both 

 of the substances RH and R'-OH were inherent in the amino acid 

 molecule; the H+ of the -COOH being exchangeable for cations and 

 the OH - of the -NH 5 OH groups being exchangeable for anions. By 

 postulating an orientation of amino acid molecules in the protoplasm 

 or plasma membrane (mosaic arrangement) Brooks was able to en- 

 visage the entry into the cell of both cations and anions along different 

 paths by a series of ion exchanges involving H+ and OH - . At a much 

 later date Steward and Street (44), on the theory that ion accumulation 

 is intimately tied up with protein synthesis in the plant, speculated that 

 RH and R'-OH may correspond to the acidic and basic groups of 

 certain phosphorylated energy-rich nitrogen compounds in the proto- 

 plasm. 



Very interesting speculations regarding the nature of R-H and 

 R'-OH are embodied in Lundegardh's theory of "anion respiration" 

 (29). According to Lundegardh there is little difficulty in accounting 

 for the properties of R-H in plants, since the protoplasm as a whole 

 is negatively charged and contains appreciable quantities of substances 

 with comparatively strong acid properties. Cations in the culture me- 

 dium therefore exchange for H+ ions in the plasma membrane and 

 proceed inward through the protoplasm by exchange along paths or 

 tracks of substances of acid dissociation. No special energy would be 

 required for this type of transport. For these reasons Lundegardh's 

 theory is chiefly concerned with the nature of R'-OH, that is, with the 

 means by which anions are absorbed and moved within the plant. 

 Accordingly, Lundegardh conjectures that ". . . the Fe-ion in the 

 hemin group of a respiratory enzyme is indeed well suited to effect 

 an anion transport, according to the following scheme 



'Fe + + + \ +e /Fe ++ \ 



3 A~ / -e \2\~ / 



"The trivalent Fe-atom attracts one more anion than the bivalent Fe- 

 atom. If the enzyme system constitutes a structural unit, in which elec- 

 trons move from one atom to another in the next molecule . . . the 



