High-affinity Ca2+-Mg2+-ATPase in kidney of euryhaline Gillichthys mirabilis: kinetics,subcellular distribution and effects of salinity |
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Institution: | 1. Department of Microbiology, Immunology and Biopharmaceuticals, National Chiayi University, Chiayi 600, Taiwan;2. Department of Ophthalmology, Chiayi Christian Hospital, Chiayi, Taiwan;1. Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California, Carretera Ensenada-Tijuana No. 3918, Zona Playitas, C.P. 22860 Ensenada, B.C., Mexico;2. Instituto de Investigaciones Oceanológicas, UABC. Carretera Ensenada-Tijuana, No. 3917, Fraccionamiento Playitas, C.P. 22860 Ensenada, Baja California, Mexico |
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Abstract: | - 1.1. Two components of Ca2+-Mg2+-ATPase are observed in kidneys of G. mirabilis. The high-affinity component has a K0.5Ca of 0.23μM; the low-affinity activity K0.5Ca is 90–110μM. The high-affinity activity requires Mg2+, displays Michaelis-Menten kinetics, has peak activity at 1.2 μM Ca2+, and is insensitive to ouabain and Na+ azide.
- 2.2. In subcellular fractions, the high-affinity component segregates with Na+-K+-ATPase and is localized predominantly in BLM. The low-affinity component is broadly distributed among membranous organelles, including brush border, and may be equivalent to alkaline phosphatase.
- 3.3. Specific activity of the high-affinity Ca2+-Mg2+-ATPase is modestly increased following adaptation of fish to FW, but total renal high-affinity activity is greatest in the hypertrophied kidneys of FW-adapted fish and is least in kidneys of fish adapted to 200% SW.
- 4.4. High-affinity Ca2+-Mg2+-ATPase may be associated with active Ca2+ transport or with regulation of intracellular Ca2+ concentration of tubular cells.
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