ENDOGENOUS RESPIRATION REFLECTS THE ENERGY LOAD IMPOSED BY TRANSPORT OF NONMETABOLIZABLE SUBSTRATES AND BY INDUCED DENOVO PROTEIN-SYNTHESISIN RHODOTORULA-GLUTINIS

Uptake of the nonmetabolizable sugars 6-deoxy-D-glucose, L-rhamnose an d L-xylose, which are taken up by a common carrier, stimulated signifi cantly cell respiration in Rhodotorula glutinis. The extra oxygen cons umption for uptake (0.5-0.7 equivalents O2/mol transported sugar) was proportional to the uptake rate and was independent of the K(T) value of the transport system. Sugars that become metabolized after inductio n, D-arabinose and methyl-alpha-D-glucoside, caused a higher stimulati on, 1.4 and 3.6 equivalents O2/mol respectively, which was reduced to 0.6 equivalents O2/Mol when de novo protein synthesis was blocked by c ycloheximide. The stimulation of respiration thus includes a fraction related purely to the energy demand for uptake and another one related to the induced de novo protein synthesis. The net uptake-induced resp iration boost was similar with all sugars under study irrespective of their transport systems. The estimated energy demand was equivalent to about 2 ATP/sugar molecule. For comparison, the amino acid analogue a lpha-aminoisobutyric acid (AIB) was also investigated; the overall ene rgy demand for its uptake corresponded to the equivalent of about 4 AT P/molecule.