Mechanism of arginine transport in Chlorella

Abstract

The incubation of Chlorella cells with glucose causes the induction of an uptake system, which is specific for the basic amino acids arginine and lysine. Both amino acids are taken up in the positively charged form and with high affinity (K _m values 2 μM and 7 μM, respectively). The transport of arginine depolarizes the membrane by 20–30 mV. The charge compensation is achieved within a few seconds after arginine addition by the proton pump, later on K⁺ efflux serves for charge compensation. No evidence for arginine-proton symport was found, neither by inhibitor studies nor by use of other Chlorella strains which have a slower-responding proton pump. The accumulation of arginine is appreciably higher than it should be according to the thermodynamic force of the membrane potential. There is, however, some evidence that a large proportion of arginine is trapped by intracellular compartments and is therefore not in equilibrium with the outside arginine.