A comparison of the toxic effects of 2‐deoxy‐D‐glucose and 2‐deoxy‐2‐fluoro‐D‐hexoses on Saccharomyces cerevisiae cells and protoplasts

Abstract

The toxicity to the cells and protoplasts of Snccharomyces cereuisim of the sugar analogues modified a t carbon 2 increases in t,he order 2-deoxy-n-glucose (DG), 2-deoxy-2-f~uoro-D-g~ucose (FG) and 2-deoxy-2-f~uoro-~-mannose (FM). The fluorohexoses, similarly as DG, behave generally as analogues of both glucose and mannose, depending on the hexose used as a carbon source in t h e medium. Relative inhibitions of glucan and mannan synthesis in protoplasts were found to be dependent more on glucose and mannose used as the growth support than on the type of the sugar analogue. Certain degree of structural relationship of fluorohexoses t o the corresponding natural hexoses was reflected in their effects on growth of intact cells. Growth on glucose was inhibited most effectively by FM, growth on mannose by PG. The data obtained support the view that the sugar analogues interfere mainly with the glucose-mannose interconversion catalyzed by hexosephosphateisomerases. A comparison of the effects of fluorohexoses and DG on t h e synthesis of extracellular invertase and intracellular n-glucosidase and alkaline phosphatase in prot,oplasts pointed to the fact t h a t all three sugar analogues tested also participate in metabolic control of enzyme synthesis.Non-fermentable analogues of glucose and niannose modified at carbon 2, 2-deoxy-D-ghcOSe (DG), 2-deoxy-2-fluoro-~-glucose (EG) and 2-deoxy-2-fluoro-u-mannose (FM) are known as potent inhibitors of growth of the yeast Saccharomyces cerevisiae (HEREDIA et al. 1964, BI.ELY et al. 1971. The analogues are taken up by the cells and phosphorylated to 6-phosphates by hexokinases (CRAMER and WOODWARD 1952, BESSEL et al. 1972). The phosphates further enter the metabolic pathways of glucose and mannose in which the six-carbon chains of the natural hexoses are preserved. All three sugar analogues mentioned were shown t o be incorporated into sugar nucleot'ides and cell wall polysaccharides of 8. cerevisiae (BIELY and BAUER 1960,1968, K R~T K~ et al. 1975, LEHLE and SCIIWARZ 1976, SCHMIDT et al. 1978. The extent of their incorporation into cell wall polysaccharides is rather low, however, their phosphate esters and nucleotides are accuniulated inside the cells and interfere severely in the synthesis of structural cell wall polysaccharides (FARKA~ et al. 1969, KUO and LAMPEN 1972, K R A T K~ et aZ. 1975, TSIOMEEKO et al. 1978. The inhibition of polysaccharide synthesis results in lysis of growing cells due t o disturbance of balanced cell wall growth (JOHNSON 1968, BIELY et al. 1973.Studies devoted t.0 the effects of UG (BIELY et aE. 1971, KRLTKY et al. 1975 and FG (BIELY et al. 1973) on growth and sonie metabolic activities of 8. cerevisiae cells and protoplasts showed that FG is more toxic than DG. Particularly t.he synthesis of cell wall glucan was found to be extremely FG-sensitive (BIELY et al. 1973). Siniilar studies with FM have not been done yet,. We considered it of interest to compare the effects of FG and FM on X. cerevisiae cells and protoplasts in order to find out to w...