Higher intracellular levels of uridinemonophosphate under nitrogen-limited conditions enhance metabolic flux of curdlan synthesis in Agrobacterium species.
Changes of intracellular nucleotide levels and their stimulatory effects on curdlan synthesis in Agrobacterium species were investigated under different culture conditions. Under nitrogen-limited conditions where curdlan synthesis was stimulated, intracellular levels of UMP were as high as 87 and those of AMP were 78 nmol/mg of cellular protein, while those under nitrogen-sufficient conditions were lower than 45 nmol/mg-protein. The levels of other nucleotides such as UDP, UTP, UDP-glucose, ADP, ATP, and ADP-glucose were lower than 30 nmol/mg-protein under both nitrogen-limited and sufficient conditions. The time profiles of curdlan synthesis and cellular nucleotide levels showed that curdlan synthesis had a positive relationship with intracellular levels of UMP and AMP. After the ammonium concentration in the medium fell below 0.1 g/L, intracellular levels of UMP and AMP increased, followed by curdlan synthesis. However, no significant changes in the specific activities of UMP kinase, UDP kinase, and UDP-glucose pyrophosphorylase were observed during cultivation. In vitro enzyme reactions for the synthesis of UDP-glucose, which serve as a precursor for curdlan synthesis, demonstrated that the synthesis of UDP-glucose increased with the increase of UMP concentration. In contrast, AMP had no effect on UDP-glucose synthesis at all. Addition of UMP in the medium increased the curdlan synthesis, whereas curdlan synthesis was inhibited in the presence of AMP. From these results, we concluded that only the higher intracellular UMP levels caused by nitrogen limitation in the medium enhance the metabolic flux of curdlan synthesis by promoting cellular UDP-glucose synthesis.
Kim
M K
MK
Bioprocess Technology Research Division, Korea Research Institute of Bioscience and Biotechnology, P.O. Box 115, Yusong, Taejon 305-600, Korea.
Lee
I Y
IY
Ko
J H
JH
Rhee
Y H
YH
Park
Y H
YH
D000249:Adenosine Monophosphate / Q000378:metabolism / Q000494:pharmacology; D003470:Culture Media / Q000494:pharmacology; D004798:Enzymes / Q000187:drug effects / Q000378:metabolism; D005936:Glucans / Q000096:biosynthesis*; D017672:Nitrogen Compounds / Q000494:pharmacology*; D009701:Nucleoside-Diphosphate Kinase / Q000187:drug effects / Q000378:metabolism; D009703:Nucleoside-Phosphate Kinase / Q000187:drug effects / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis / Q000187:drug effects*; D012231:Rhizobium / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase / Q000187:drug effects / Q000378:metabolism; D014542:Uridine Monophosphate / Q000378:metabolism* / Q000494:pharmacology; D047071:beta-Glucans
D003470:Culture Media; D004798:Enzymes; D005936:Glucans; D017672:Nitrogen Compounds; D011135:Polysaccharides, Bacterial; D047071:beta-Glucans; D000249:Adenosine Monophosphate; C038459:curdlan; D014542:Uridine Monophosphate; C029260:uridine diphosphate kinase; C023276:uridine monophosphate kinase; D009703:Nucleoside-Phosphate Kinase; D009701:Nucleoside-Diphosphate Kinase; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase