Article Abstract:
The cellular slime mold Dictyoselium discoideum varies the amount of glutamine synthetase it produces as it goes through different stages of its life cycle. Slime mold glutamate synthetase, which enables the cell to metabolize ammonia for the synthesis of amino acids, occurs increasingly when the mold differentiates from vegetative cells, with more of the enzyme concentrated in the prespore cells. The enzyme was characterized as having an optimum pH between 7.8 and 8.2, a temperature optimum of 45 degrees Celsius and kinetic activity rates of 5.9 millimoles for glutamine.
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Article Abstract:
A model in which glutamine synthetase (GS) in prespore cells of Dictyostelium discoideum act as a sink for ammonia is presented. The absence of ammonia permits the activation of protein kinase A by the osmotically sensitive adenylyl cyclase aggregation protein (ACA), a reaction that induces spore formation. A decrease in GS and ACA activities after spore formation is balanced by the appearance of the dormancy-inducing adenylyl cyclase osmosensor for germination that is stimulated by the presence of ammonia.
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Article Abstract:
The Thiobacillus ferrooxidans alaS gene was cloned, sequenced and compared to other alanyl-tRNA synthetase genes. Its expression in Escherichia coli and T. ferrooxidans was also analyzed. E. coli and T. ferrooxidans were found having the same genomic organization of recA-recX-alaS. However, it was observed that the recA and alaS genes cannot be transcribed from their own promoters in E.coli.
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