Effect of NaCl on kinetics ofd-glucosamine uptake in yeasts differing in halotolerance
The initial rate ofd-glucosamine uptake by the non-halotolerant yeastSaccharomyces cerevisiae was approximately halved as the apparent half saturation constant (Km) and the apparent maximum velocity (Vmax) changed from 6.6mm to 16.4mm and from 22 μmol · g−1 · min−1 to 16 μmol · g−1 · min−1, respectively, when the salinity in the medium was increased from zerom to 0.68m NaCl. Corresponding changes in a high affinity transport system in the halotolerant yeastDebaryomyces hansenii were from 1.1mm to 4.6mm and from 3.1 μmol · g−1 · min−1 to 4.5 μmol · g−1 · min−1, implying a practically unchanged transport capacity. In 2.7m NaCl, Km and Vmax in this system were 24.5mm and 1.1 μmol · g−1 · min−1, respectively, representing a marked decrease in transport capability. Nevertheless, the degree of affinity in this extreme salinity must still be regarded as noteworthy. In addition to the high affinity transport system inD. hansenii, a low affinity system, presumably without relevance ind-glucosamine transport, was observed.
KeywordsTransport System Initial Rate Maximum Velocity Marked Decrease Transport Capacity
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