Fig. 3.
Pi requirement for spontaneous extracellular catabolism of purine ribonucleosides. (A) Cytosol only without KH2PO4 (control) or cytosol only with added KH2PO4. (B–D) Cytosol plus an added purine ribonucleoside and NADP+ without KH2PO4 (control) or with added KH2PO4. Presence of a purine ribonucleoside carbon chain fuel source and NADP+ added to individual experiments are indicated above each panel (B–D). NADPH generation was determined by measurement of GSH produced from 3mM GSSG added to all experiments (A–D). X-axes show control experiments (no Pi added) and experiments supplemented with Pi. Y-axes show on the left of panel μM GSH generated and on the right of the panel μM Pi added or consumed (coded bars). 75 ng/μl cytosolic protein added to all experiments (A–D). Incubations were for 1200 min at pH 6.9 at 37°. Data are the mean (±SEM) of three separately performed experiments.