Transport of lysine and hydroxylysine in Streptococcus faecalis

Bioenergetics and solute transport in lactococci

During the last few years the studies about the physiology and bioenergetics of lactic acid bacteria during growth and starvation have evolved from a descriptive level to an analysis of the molecular events in the regulation of various processes. Considerable progress has been made in the understanding of the modes of metabolic energy generation, the mechanism of homeostasis of the internal pH, and the mechanism and regulatory processes of transport systems for sugars, amino acids, peptides, and ions. Detailed studies of these transport processes have been performed in cytoplasmic membrane vesicles of these organisms in which a foreign proton pump has been introduced to generate a high proton motive force.

Transport of branched-chain amino acids in membrane vesicles of Streptococcus cremoris

The kinetics, specificity, and mechanism of branched-chain amino acid transport in Streptococcus cremoris were studied in a membrane system of S. cremoris in which beef heart mitochondrial cytochrome c oxidase was incorporated as a proton motive force (delta p)-generating system. Influx of L-leucine, L-isoleucine, and L-valine can occur via a common transport system which is highly selective for the L-isomers of branched chain amino acids and analogs. The pH dependency of the kinetic constants of delta p-driven L-leucine transport and exchange (counterflow) was determined. The maximal rate of delta p-driven transport of L-leucine (Vmax) increased with increasing internal pH, whereas the affinity constant increased with increasing external pH. The affinity constant for exchange (counterflow) varied in a similar fashion with pH, whereas Vmax was pH independent. Further analysis of the pH dependency of various modes of facilitated diffusion, i.e., efflux, exchange, influx, and counterflow, suggests that H+ and L-leucine binding and release to and from the carrier proceed by an ordered mechanism. A kinetic scheme of the translocation cycle of H+-L-leucine cotransport is suggested.

Metabolism of 5-hydroxylysine in Pseudomonas fluorescens

Hydroxylysine is metabolized via two routes by a Pseudomonas fluorescens strain as shown by the oxidation of selected intermediates. Hydroxy-L-lysine is oxidized via a pathway analogous to the monooxygenase pathway for L-lysine, and data suggest that at least some of tthe enzymes are those involved in the metabolism of L-lysine. Hydroxy-L-lysine is also converted by a racemase to allohydroxy-D-lysine, which is then degraded via a pathway analogous to, but different from, that described for D-lysine, involving hydroxy-L-pipecolate, 2-amino-5-hydroxyadipate, and 2-hydroxyglutarate. Data obtained with mutants unable to oxidize L-pipecolate suggest that the enzymes for the metabolism of hydroxy-L-pipecolate are distinct from those for L-pipecolate. Studies on D- and L-lysine degradation have shown that the previously described pathways for these compounds are present in this soil pseudomonad.

Uptake and utilization of glutamic acid by Cryptococcus albidus

Cryptococcus albidus utilizes glutamate as a sole carbon source. The kinetics of uptake of this amino acid were studied. l-Glutamic acid was taken up by two saturable systems: a high affinity system with a Michaelis constant (K(m)) of 1.15 x 10(-5) M and a V(max) of 0.049 mumol per mg per h and a low affinity system with a K(m) of 2.5 x 10(-3) M and a V(max) of 3.61 mumol per mg per h. Both systems possessed characteristics of active transport which were dependent on temperature and pH and which required metabolic energy. Uptake was inhibited at 37 C but the temperature-sensitive step was reversible. Chemical fractionation of cells with 5% trichloroacetic acid showed that glutamic acid initially entered a soluble pool which decreased after 1 h as the amino acid was incorporated into the protein and nucleic acid fractions of the yeast. Some of the glutamate was completely oxidized and could be recovered as (14)CO(2). Therefore, the amino acid was also used as an energy source.