542 E. HEINZ 
step of glycine uptake which follows after, and is more specific than the transport 
process. 
I would like to add a few comments on the action of various ions, in particular H+ 
ions and alkali ions, on glycine accumulation, which had been previously observed 
by CHRISTENSEN ef al.'®. With KROMPHARDT we found H* ions to inhibit the influx 
instantaneously and reversibly’. The action is likely to concern the transport me- 
chanism directly rather than via metabolic inhibition. Plotting glycine influx versus 
100 
50 
°° 20.9uM Glycine 
+,x 0.86uM Glycine 
°/o Of maximal influx 

5.0 60 7.0 80 pH 
Fig. 5. Effect of H* ions on glycine influx at different concentrations of extracellular glycine. 
The flux values are corrected for a small pH-independent fraction of the influx. The maximum 
influx is obtained by extrapolation®. (Fig. reproduced by permission of Springer-Verlag). 
pH and taking into account a constant pH-independent fraction of the influx we 
obtain a titration curve with an inflexion point around pH 6.9. This recalls a similar 
pH dependence of certain enzyme reactions. Since this inflexion point is not shifted 
by greatly increasing the glycine concentration there is no competition between 
substrate and H* ion for the same point of attachment (Fig. 5). We assume that 
ee 
E 


Glycine-influx 
at varying extracellular [K+] 
Relative glycine influx 
re 
ad 

o [Nat] _ increasingly replaced by [«*] 
a[Na‘|. =constant at 90 mequiv/| 

1°°5 4100 45) 207 S530 S5"40F 4550055" cbi7s5 
[k*l. (medium) mequiv/ | 
Fig. 6. Effect of extracellular K+ concentration on glycine influx. Upper curve, K+ is increased 
at the expense of Nat. Lower curve, extracellular Na+ remains constant at 60 mequiv./l. Choline 
ions are used to make up for deficient Na+ ions!*. 
References p. 544 
