Although the triose-phosphate isomerase (Tpi), GapA, phosphoglycerate kinase (Pgk), and enolase (Eno) are all encoded from the gap operon , our proteome data showed a significantly lower expression selleck chemicals llc only for GapA, Pgk and Eno. In addition, expression of the L-lactate dehydrogenase (LdhL) responsible for the reduction of pyruvate to lactic acid was observed
to be lower in the two strains. The bacterium alters its pyruvate metabolism growing on ribose compared to glucose, possibly since during ribose utilization, more ATP is generated from pyruvate per ribose unit when MI-503 ic50 Acetate is produced than when lactate is produced . The up-regulated pyruvate oxidases convert pyruvate into acetyl-phosphate, and the PDC catalyses the transformation of pyruvate to acetyl-CoA (Figure 2). The increased GlpD enzyme belongs to the glycerol/glycerolipid catabolic pathway, a pathway linked to membrane properties as glycerol-3-phosphate can be converted to phosphatidic acid, which leads to membrane phospholipid synthesis. Also when exposed to low temperature, this protein shows an increased expression in L. sakei . Modified membrane properties could potentially also exist as a response to the higher level of acetate produced when utilizing ribose. Acetate has a higher antimicrobial
effect than lactate, with pKa values of 4.74 and 3.86, respectively, CDK inhibitor and the proportion of antimicrobial undissociated acetic acid molecules is increased as the pH is lowered. The glpD gene is associated in a glp
operon with glycerol kinase (glpK), which also showed an increased expression on ribose, and glycerol uptake facilitator protein (glpF) PI3K inhibitor genes . The role of CcpA in CCR in L. plantarum has previously been established, and CcpA was shown to mediate regulation of the pox genes encoding pyruvate oxidases [52, 53]. Rud  observed an up-regulation of several genes and operons including the pox genes, the pdh operon encoding the PDC, and the glp operon, during growth on ribose compared with glucose. As putative cre sites  were identified in promoter regions, their expression was suggested to be regulated by CcpA-mediated CCR. The putative cre site found preceding rbs in L. sakei , could indicate that this bacterium possesses global regulation mediated by CcpA. In an rbsR mutant overexpressing RbsUDK, the growth on ribose was not accelerated, whereas in a ptsI mutant, the transcription of rbsUDK was not modified, but transport and phosphorylation of ribose increased. Thus it was concluded that the PTS negatively controls ribose utilization, by a direct or indirect way [17, 22]. Nevertheless, a change in expression of the PTS enzymes could not be detected in our ribose 2-DE gels. Further experiments are needed to elucidate the mechanism by which the rbs operon is regulated.