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Phosphate Source (phosphate + source)

Distribution by Scientific Domains

Life Sciences	60%

Selected Abstracts

Crystal structure and kinetic mechanism of aminoglycoside phosphotransferase-2,-IVa

PROTEIN SCIENCE, Issue 8 2010
Marta Toth
Abstract Acquired resistance to aminoglycoside antibiotics primarily results from deactivation by three families of aminoglycoside-modifying enzymes. Here, we report the kinetic mechanism and structure of the aminoglycoside phosphotransferase 2,-IVa (APH(2,)-IVa), an enzyme responsible for resistance to aminoglycoside antibiotics in clinical enterococcal and staphylococcal isolates. The enzyme operates via a Bi-Bi sequential mechanism in which the two substrates (ATP or GTP and an aminoglycoside) bind in a random manner. The APH(2,)-IVa enzyme phosphorylates various 4,6-disubstituted aminoglycoside antibiotics with catalytic efficiencies (kcat/Km) of 1.5 × 103 to 1.2 × 106 (M,1 s,1). The enzyme uses both ATP and GTP as the phosphate source, an extremely rare occurrence in the phosphotransferase and protein kinase enzymes. Based on an analysis of the APH(2,)-IVa structure, two overlapping binding templates specifically tuned for hydrogen bonding to either ATP or GTP have been identified and described. A detailed understanding of the structure and mechanism of the GTP-utilizing phosphotransferases is crucial for the development of either novel aminoglycosides or, more importantly, GTP-based enzyme inhibitors which would not be expected to interfere with crucial ATP-dependent enzymes. [source]

Growth of the vacuoleless mutant of Tetrahymena thermophila NP1 in phytate

THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2005
SAMANTHA WEBB
Phytate, the salt form of phytic acid, is the major store of phosphate in seeds and grain. Since non-ruminant farm animals poorly digest phytate, it is also a source of environmental phosphate contamination in agricultural areas. We are using Tetrahymena, a ciliated protist with multiple routes for nutrient assimilation, as a model to investigate the contribution of heterotrophic protists to the environmental cycling of phosphate from phytate. This ciliate has the ability to grow on phytate as the sole phosphate source (Ziemkiewicz, H. T., Johnson, M. D. & Smith-Somerville, H. E. 2002. J. Eukaryot. Microbiol., 49:428). Tetrahymena thermophila NP1, a temperature-sensitive vacuoleless mutant (ATCC #50202), provides a way to separate membrane transport from uptake through phagosomes, and to assess the importance of each mechanism. This cell grows equally well at the permissive and non-permissive temperatures with either phytate or inorganic phosphate as the phosphate source. Our results demonstrate that phagosomes are not required to use the phosphate from phytate. [source]

Precambrian animal life: Taphonomy of phosphatized metazoan embryos from southwest China

LETHAIA, Issue 2 2005
DORNBOS STEPHEN
Phosphatized fossils from the Neoproterozoic Doushantuo Formation have provided valuable insight into the early evolution of metazoans, but the preservation of these spectacular fossils is not yet fully understood. This research begins to address this issue by performing a detailed specimen-based taphonomic analysis of the Doushantuo Formation phosphatized metazoan embryos. A total of 206 embryos in 65 thin sections from the Weng'an Phosphorite Member of the Doushantuo Formation were examined and their levels of pre-phosphatization decay estimated. The data produced from this examination reveal a strong taphonomic bias toward earlier (2-cell and 4-cell) cleavage stages, which tend to be well-preserved, and away from later (8-cell and 16-cell) cleavage stages, which tend to exhibit evidence for slight to intense levels of organic decay. In addition, the natural abundances of these embryos tend to decrease with advancement in cleavage stage, and no evidence of more advanced (beyond 16-cell) cleavage stages or eventual adult forms were found in this study. One possible explanation for this taphonomic bias toward early cleavage stages is that later cleavage stages and adult forms were more physically delicate, allowing them to be more easily damaged during burial and reworking, allowing for more rapid decay. The spectacular preservation of these embryos was probably aided by their likely internal enrichment in phosphate-rich yolk, which would have caused their internal dissolved phosphate levels to reach critical levels with only miniscule organic decay, thereby hastening phosphatization. If internal sources of phosphate did indeed play a role in the phosphatization of these embryos, it may explain their prolific abundance in these rocks compared to other phosphatized fossils as well as indicating that metazoans lacking such internal phosphate sources were likely much more difficult to preserve. The phosphatic fossils of the Doushantuo Formation, therefore, provide an indispensable, yet restricted, window into Neoproterozoic life and metazoan origins. [source]

Carboxylate composition of root exudates does not relate consistently to a crop species' ability to use phosphorus from aluminium, iron or calcium phosphate sources

NEW PHYTOLOGIST, Issue 1 2007
Stuart J. Pearse
Summary ,,The relationship between carboxylate release from roots and the ability of the species to utilize phosphorus from sparingly soluble forms was studied by comparing Triticum aestivum, Brassica napus, Cicer arietinum, Pisum sativum, Lupinus albus, Lupinus angustifolius and Lupinus cosentinii. ,,Plants were grown in sand and supplied with 40 mg P kg,1 in the sparingly soluble forms AlPO4, FePO4 or Ca5OH(PO4)3, or as soluble KH2PO4; control plants received no P. ,,The ability to utilize sparingly soluble forms of P differed between forms of P supplied and species. Pisum sativum and C. arietinum did not access AlPO4 or FePO4 despite releasing carboxylates into the rhizosphere. ,,Species accessed different forms of sparingly soluble P, but no species was superior in accessing all forms. We conclude that a single trait cannot explain access to different forms of sparingly soluble P, and hypothesize that in addition to carboxylates, rhizosphere pH and root morphology are key factors. [source]