Genomic rearrangements in the aspA-dcuA locus of Propionibacterium freudenreichii are associated with aspartase activity.

Propionibacterium freudenreichii is crucial in Swiss-type cheese manufacture. Classic propionic acid fermentation yields the nutty flavor and the typical eyes. Co-metabolism of aspartate pronounces the flavor of the cheese; however, it also increases the size of the eyes, which can induce splitting and reduce the cheese quality. Aspartase (EC 4.3.1.1) catalyzes the deamination of aspartate, yielding fumarate and ammonia. The aspartase activity varies considerably among P. freudenreichii strains. Here, the correlation between aspartase activity and the locus of aspartase-encoding genes (aspA ) and dcuA encoding the C4-dicarboxylate transporter was investigated in 46 strains to facilitate strain selection for cheese culture. Low aspartase activity was correlated with a particular genomic rearrangement: low in vitro aspartase activity always occurred in strains with gene clusters aspA - dcuA where the dcuA was frameshifted, producing a stop codon or was disrupted by an ISL3-like element. The low aspartase activity could be due to the protein sequence of the aspartase or a dysfunctional DcuA. The highest values of aspartase activity were detected in strains with aspA1 - aspA2-dcuA with a DcuA sequence sharing 99.07 - 100% identity with the DcuA sequence of strain DSM 20271 T and an additional C4-dicarboxylate transporter belonging to the DcuAB family.

Skeletal muscle protein synthesis after active or passive ascent to high altitude.

INTRODUCTION: The effects of acute exposure to high altitude on muscle protein synthesis rates in human volunteers were examined after active and passive ascent. METHODS: Measurements were made initially at low altitude (550 m) and again after ascent to high altitude (4,559 m). To be able to separate the contribution of physical exercise, one group was flown by helicopter (air group, N=8), whereas the other group climbed to high altitude (foot group, N=9). Fractional rates of muscle protein synthesis rates (FSR) were determined from the incorporation of isotope into protein after injection of [H5ring] phenylalanine. RESULTS: In the air group, there was no change in FSR at high altitude, whereas in the foot group, there was a 35% increase in FSR (P<0.05 for interaction) measured 19-23 h after the end of climbing. At high altitude, the degree of hypoxia and alkalosis were not different between the groups. The plasma concentration of insulin-like growth factor-1, free thyroxin, free triiodothyronine, and thyroid-stimulating hormone were not different between the groups. Urinary 24-h cortisol excretion increased significantly in both groups after ascent, but the increase in the foot group was significantly higher compared with the air group. CONCLUSION: Physical exercise appeared to be responsible for the observed increase in muscle FSR. The significantly higher increase of 24-h cortisol excretion in the foot group suggests that the increase in FSR occurred despite higher levels of glucocorticoids, which generally affect muscle protein turnover by inhibiting protein synthesis.