The effect of flavomycin on the synthesis and transfer of lipid-linked saccharides in pig brain

Abstract

Particulate membrane fractions from pig brain catalyze the synthesis of lipid-linked sugar derivatives of the dolichyl phosphate pathway. Flavomycin, a phosphoglycolipid antibiotic produced by various species of streptomycetes, interferes with the formation of these glycolipids to a different extent. The formation of dolichyl phosphate glucose was most susceptible to the antibiotic, being blocked by about 50% in the presence of 0.2 mM-flavomycin, whereas the synthesis of dolichyl diphosphate N-acetyl-glucosamine, dolichyl diphosphate chitobiose and dolichyl diphosphate chitobiosyl mannose required higher concentrations to achieve a comparable inhibition. Although the formation of dolichyl phosphate mannose was hardly affected, the accumulation of oligosaccharides with 5-7 sugar units was observed when dolichyl diphosphate oligosaccharides were synthesized with GDP-[14]mannose in the presence of 1 mM-flavomycin. The inhibition of the synthesis of larger-sized oligosaccharides, mediated by lipid-bound mannose, was apparently not caused by an actual deficiency in dolichyl phosphate mannose. At flavomycin concentrations that inhibited the formation of dolichyl phosphate glucose by 50%, the transfer of lipid-linked saccharides to either the hexapeptide Try-Asn-Gly-Thr-Ser-Val or endogenous protein acceptors was hardly influenced. The mode of action of flavomycin is still obscure but seems not to be of a competitive nature, since the inhibition was unaffected by increasing concentrations of dolichyl phosphate. Besides a direct interaction of the antibiotic with some transferases, a non-specific incorporation into the membrane and alteration of its properties might be responsible for those inhibitory effects on all enzymes which were observed at high concentrations of flavomycin.