Does gene palB regulate the transcription or the post-translational modification of Pi-repressible phosphatases of Aspergillus nidulans?

When grown on low-Pi medium, the chaA1 pabaA1 palB7 mutant of Aspergillus nidulans excretes an acid phosphatase with steady-state kinetic properties, temperature sensitivity and electrophoretic mobility different from those of the enzyme excreted by the pabaA1 strain. The enzyme excreted by the pabaA1 strain at pH 6.5 showed PNP-P activity with negative cooperativity (K0.5 = 0.87 + or - 0.06 mM, n = 0.68 + or - 0.03) whereas the enzyme excreted by the chaA1 pabaA1 palB7 mutant showed Michaelian kinetics (Km = 0.46 + or - 0.03 mM, n = 1.00 + or - 0.02). The apparent half-lives at 60§C, pH 5.5, of acid phosphatase excreted by the pabaA1 and chaA1 pabaA1 palB7 strains were 58.6 + or - 4.9 min and 21.5 + or - 1.8 min, respectively. Furthermore, the electrophoretic mobility of acid phosphatases excreted by the palA1, palB7, palC4, palE11 and palF15 mutants of A. nidulans was altered and differed from the electrophoretic mobility of the enzyme excreted by the wild-type strain. Also, the palB7 mutation altered the electrophoretic pattern of acid phosphatases synthesized on high-Pi medium. These results are compatible with the post-translational modifications in the Pi-repressible phosphatases rather than with the action of gene palB in controlling the transcription of structural genes of these enzymes

Kinetic studies of nitrite uptake by Aspergillus nidulans

1. In the filamentous mold Aspergillus nidulans, net nitrite uptake is inducible by nitrate and nitrite, is probably different from the nitrate uptake system and is partially repressed by ammonium. 2. The concentration dependence of net nitrite uptake by the biA1 facA303 strain of A. nidulans shows a saturation kinetics with an apparent Km value of 0.64 mM. 3. Strains of A. nidulans carrying the nihA1 and nihA1 chlA14 mutations considerably reduced the affinity of the nitrite uptake system for the substrate when nitrite concentrations ranging from 2.5 mM to 10.0 mM were tested (apparent Km values of 5.9 mM and 23.6 mM, respectively). 4. These results suggest that the toxic effect of nitrite on A. nidulans is due to enhanced nitrite uptake by nihA strains when high concentrations are present in the medium