| Abstract: | Glucose and related non-metabolizable analogs were transported into cells of Stichococcus bacillaris Naeg. By a specific and active transport system. Glucose transport capacity was stimulated eight-fold by incubation in medium of low osmotic potential (0.09 osM). Stimulation occurred over 24 h in the dark and over 72 h in low osmotic medium. Inhibition of protein synthesis prevented any transport, stimulation from occurring. Kinetic studies revealed that the stimulation caused an increase in Ike maximal velocity of transport and did not affect the half-saturation constant for transport. It was concluded that incubation of cells in the dark or in low osmolar medium induces a synthesis of the transport system. The glucose analog 2-deoxy-D-glucose was only phosphorylated to a limited extent upon entry into the cells, and the free sugar accumulated linearly in dark pre-incubated tells for a period of at least six minutes to reach an intracellular/extracellular concentration ratio of almost 300. Glucose, in contrast, was rapid h converted to sucrose and other cell constituents. Cells incubated 24 h with, glucose or 6-deoxy-D-glucose did not exhibit any altered transport system activity. Cells incubated 24 h with 7 mM dibutyryl cAMP exhibited a 2.5-fold stimulation of transport activity. No stimulation was observed in cells treated only 30 min with dibutyryl cAMP. |
