Transport of Biosynthetic Intermediates: Homoserine and Threonine Uptake in Escherichia coli
AUTOR(ES)
Templeton, Bonnie A.
RESUMO
Although amino acid transport has been extensively studied in bacteria during the past decade, little is known concerning the transport of those amino acids that are biosynthetic intermediates or have multiple fates within the cell. We have studied homoserine and threonine as examples of this phenomenon. Homoserine is transported by a single system which it shares with alanine, cysteine, isoleucine, leucine, phenylalanine, threonine, tyrosine, and valine. The evidence for this being the sole system for homoserine transport is (i) a linear double-reciprocal plot showing a homoserine Km of 9.6 × 10−6 M, (ii) simultaneous reduction by 85% of homoserine and branched-chain amino acid uptake in a mutant selected for its inability to transport homoserine, and (iii) simultaneous reduction by 94% of the uptake of homoserine and the branched-chain amino acids by cells grown in millimolar leucine. Threonine, in addition to sharing the above system with homoserine, is transported by a second system shared with serine. The evidence for this second system consists of (i) incomplete inhibition of threonine uptake by any single amino acid, (ii) only 70% loss of threonine uptake in the mutant unable to transport homoserine, and (iii) only 40% reduction of threonine uptake when cells are grown in millimolar leucine. In this last case, the remaining threonine uptake can only be inhibited by serine and the inhibition is complete.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=246578Documentos Relacionados
- Transport of Biosynthetic Intermediates: Regulation of Homoserine and Threonine Uptake in Escherichia coli
- Role of purine biosynthetic intermediates in response to folate stress in Escherichia coli.
- Iron Transport in Escherichia coli: Uptake and Modification of Ferrichrome
- Homoserine Kinase from Escherichia coli K-12: Properties, Inhibition by l-Threonine, and Regulation of Biosynthesis
- Mechanistic studies of glutamine synthetase from Escherichia coli: kinetic evidence for two reaction intermediates in biosynthetic reaction.