SALT ABSORPTION AND METABOLISM 



87 



MEDIUM 



A' 



CYTOPLASM 



r 



y-glutamyl peptides with 

 "free ocidic ond basic 

 groups moy bind anions 

 ond cations 



f 



E 



Glutomyl peptides act as 

 carriers of bound ions and 

 omino-acids to a nucleic 

 acid templote 



L 



Glutamic acid regenerates 

 . y-glu!amyl peptides witti 

 utilisation of ATP 



m. 



Protein peeled off as a-amino- 

 ocid linKs are formed, releasing 

 ions into ttie vocuole 



4 



m. 



Amino acid residues derived 

 from peptides are aftoctied 

 to a nucleic acid template: 

 ions remain bound 



J 



VACUOLAR 

 SAP 



•*- A" 



(a) 



MEDIUM 





K*. 



MEMBRANE 



Lecithin 



0" 



CHg 

 CHg 

 O 

 — P = 







CH- 

 CHo- 



Choline 

 esterase 



Lecithinose 

 > 



-0 R, 



-0 R 



Acetylcholine 



Choline 



acetyiase 



+ATP 



Choline 



+ 



-0 CHj 



-0 CH 



CH,- 



OH 



-P- 



I 







-OH 



INNER 



AQUEOUS 



PHASE 



-^K* 



-»-A' 



Phosphatidic acid 



(b) 



Fig. 31. Carrier mechanisms in which ATP is imphcated 

 a. A mechanism hnking salt uptake to protein synthesis (redrawn from 

 Steward and Millar, 1954); b. A cyclic mechanism of active transport involving 

 lecithin as an amphoteric carrier (redrawn from Bennet-Clark, 1956). 



