Fig. 4
From: A synthetic metabolic network for physicochemical homeostasis
Control of futile hydrolysis of arginine and pH homeostasis. The internal composition of the vesicles at the start of the experiment is given in Fig. 2a (enzymes) and Table 2 (ions, metabolites) and the preparation of vesicles is given in protocol A1, unless specified otherwise. a External concentration of metabolites (protocol B6): arginine (blue circles), citrulline (pink triangles), ornithine (yellow diamonds), and NH3 (black squares), as measured by HPLC in vesicles treated with 25 µM pCMBS. Five millimolar arginine was added at t = 0. b Schematic representation of arginine breakdown; the futile hydrolysis of arginine and arginine/citrulline exchange are depicted by bold and dashed arrows, respectively. c Stopped-flow fluorescence measurements to determine the permeability of the vesicles for NH4Cl (blue trace), NH4-acetate (black trace), potassium phosphate (pink trace) and sodium acetate (yellow trace); pyranine inside the vesicles was used as pH indicator (n ≥ 2). d Internal pH change (protocol B4) of arginine-metabolizing vesicles with either 5 mM Mg-ADP (protocol A1; blue trace) or 15 mM Mg-ADP on the inside (protocol A3; black trace). Five millimolar arginine was added at t = 0 (n = 2). e Homology model of OpuA and structure of the compatible solute glycine betaine. Glycine betaine import via OpuA consumes the ATP as indicated in (b)
