GLYCINE TRANSPORT BY THE RED-CELLS OF CHANNEL CATFISH

In humans, glycine enters the red cell via four distinct plasma membra ne carrier systems. The purpose of the present experiments was to meas ure the mode of transport of glycine by channel catfish (Ictalurus pun ctatus) red cells. About 54% of the glycine was transported by system L, while 16.1% of the glycine was transported by system Gly. A further 15.6% of transport was via system ASC and system ase together. An uni dentified Na+-independent system was responsible for the transport of 7.2% of the glycine. No solute appeared to be carried into the cell by band 3. The remainder of the glycine entered the cell by diffusion. T he Na+-independent system exhibited a K-t value of 57 +/- 12 (mean +/- standard deviation) mu M and V-max of 142 +/- 27 nmol . g hemoglobin( -1). min(-1) (this compares with system L, which exhibited a K-t value of 65 +/- 21 mu M and V-max of 516 +/- 117 nmol . g hemoglobin(-1). m in(-1)). These results demonstrate that channel catfish red cells are capable of transporting glycine by three of the four transporters invo lved in human red cells, although the relative contributions differ ma rkedly, and by an additional unidentified transport system not requiri ng Na+. The differences in glycine transport between human and catfish red cell membranes can be attributed to evolutionary influences.