[Nonesterified fatty acids (NEFA)].
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Adolescent↗
Biomedical subjects
J Guardiola
Publications and source records attributed to J Guardiola.
Escherichia coli K-12 mutants altered in the transport systems for oligo- and dipeptides.
Two mutants of Escherichia coli K-12, defective in the oligopeptide and dipeptide transport system, are described. A mutant defective in the oligopeptide transport system (opp-1) was isolated as resistant to the inhibitory action of triornithine; this mutant is also resistant to glycylglycylvaline and does not concentrate (14)C-glycylglycylglycine, although it is still as sensitive as the parental strain to glycylvaline and valine. Starting from the opp-1 strain, a mutant defective also in the dipeptide transport system (dpp-1) was isolated; this mutant is resistant to the inhibitory action of glycylvaline, valylleucine, and leucylvaline and does not concentrate (14)C-glycylglycine, although it is still as sensitive as the parental strain to valine. The apparent kinetic constants for oligopeptide and dipeptide transport were measured. The opp marker is co-transducible with trp at 27 min on the E. coli genetic map. The dpp locus is separated from opp and is located between proC (10 min) and opp.
Carbon Radioisotopes↗
The importance of calcium and magnesium ions in serum and cerebrospinal fluid during cardiopulmonary bypass.
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Animals↗
Escherichia coli K-12 mutants altered in the transport of branched-chain amino acids.
Two mutants of Escherichia coli K-12 are described which are resistant to the inhibition that valine exerts on the growth of E. coli. These mutants have lesions at two different loci on the chromosome. One of them, brnP, is linked to leu (87% cotransduction) and is located between leu and azi represented on the map at 1 min; the other, brnQ, is linked to phoA (96% cotransduction), probably between proC and phoA and represented at 10 min. These mutants are resistant to valine inhibition but are sensitive to dipeptides containing valine. Since it is known that dipeptides are taken up by E. coli through a transport system(s) different from those used by amino acids, this sensitivity to the peptides suggests an alteration in the active transport of valine. The mutants are resistant to valine only if leucine is present in the growth medium; the uptake of valine is less in both mutants than it is in wild-type E. coli, and it is reduced even further if leucine is present. Under these conditions the total uptake of valine is almost completely abolished in the brnQ mutant. The brnP mutant takes up about 60% as much valine as does the wild type, but no exogenous valine is incorporated into proteins. The apparent K(m) and V(max) of isoleucine, leucine, and valine for the transport system are reported; the brnP mutant, when compared to the wild type, has a sevenfold higher K(m) for isoleucine and a 17-fold lower K(m) for leucine; the V(max) for the three amino acids is reduced in the brnQ mutant, up to 20-fold for valine. The transport of arginine, aspartic acid, glycine, histidine, and threonine is not altered in the brnQ mutant under conditions in which that of the branched amino acids is. Evidence is reported that O-methyl-threonine enters E. coli through the transport system for branched amino acids, and that thiaisoleucine does not.
Amino Acids↗