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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Some biochemical properties of actomyosin and myosin from elasmobranchs, Squalus acanthias and Raja tengu are compared with those of a freshwater (Cyprinus carpio) and a marine teleost (Seriola quinquiradiata). Whereas Ca2+-ATPase of teleost actomyosins are more stable in the absence of urea, the reverse is true for elasmobranchs up to 1.0 M urea. In contrast to that of teleosts, the Mg2+-ATPase of S. acanthias actomyosin shows an activation in the presence of urea, where as that of R. tengu persists. Below 1.0 M urea, there is low incorporation of DTNB into thiols of elasmobranch myosins, and losses in alpha-helicity are reversible up to 5.0 M urea. The results, thus, demonstrate that for a certain concentration of urea, elasmobranch myofibrillar proteins may exhibit a group specific tolerance to urea.
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PMID:Urea tolerance of myofibrillar proteins of two elasmobranchs: Squalus acanthias and Raja tengu. 243 54

Mg2+-ATPase activity was identified in the cytosol of human erythrocytes. A partial purification of this activity was achieved by an initial DEAE-Sephadex column chromatography, followed by gel filtration on Sephadex G-100 and then a second DEAE-Sephadex chromatography procedure. The enzyme appeared in the void volume of the Sephadex G-100 column and was retained on an Amicon XM100A ultrafiltration membrane. The molecular weight of the enzyme was estimated to be 113 000 from SD gels. The above purification protocol yielded an enzyme with an optimal pH between 7.6 and 8.2. The enzyme activity increased linearly between 30 and 44 degrees C. It was stable for several months at -20 degrees C. Magnesium was essential for activity, but the rate attainable with Mn2+ was at least as great as that due to Mg2+. No other divalent cation was able to substitute for Mg2+ or Mn2+. Neither low nor high Ca2+ concentrations significantly affected the enzymatic activity. Substrate specificity studies showed that ATP was the preferred substrate followed by CTP (46% of the rate produced by ATP). Hydrolysis of GTP, UTP, ITP and ADP was less than 10% of the rate seen with ATP. No phosphatase, pyrophosphatase, phosphodiesterase, hexokinase, phosphofructokinase or adenylate cyclase activity could be detected in this enzyme preparation. Calmodulin, which stimulates the (Ca2+ + Mg2+)-ATPase of the human erythrocyte membrane, failed to enhance the Mg2+-ATPase activity. Of considerable interest, the activity of this Mg2+-ATPase was enhanced approximately 5-fold by low concentrations of mercuric ion, p-hydroxymercuribenzoate and DTNB, but was much less sensitive to iodoacetamide.
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PMID:Partial purification and characterization of a novel Mg2+-dependent ATPase present in the cytosol from human erythrocytes. 615 Jul 30

Myosins were isolated from the ordinary (white) and dark (red) muscles of yellowtail, Seriola quinqueradiata, and the pH-dependency of ATPase activity, along with some physicochemical properties, was examined. The ordinary muscle myosin contained three kinds of light chain (A1, DTNB and A2 light chains), the molecular weights of which were 28,000, 20,000, and 16,000, respectively. The dark muscle myosin possessed only two kinds of light chain (D1 and D2), the molecular weights of which were 26,000 and 20,000 respectively. These ordinary and dark muscle myosins resemble the fast and slow muscle myosins of the higher vertebrate, respectively, in light chain pattern. The pH optima of the ordinary muscle myosin Ca2+-ATPase activity appeared at 6-6.5 and 9-10, irrespective of whether the enzyme reaction was started by the addition of ATP to the preincubated reaction mixture containing myosin (method I), or vice versa (method II). In the case of the dark muscle myosin, a small peak appeared at around pH 8.5 on the alkaline side when the activity was assayed by method I, whereas a prominent peak appeared at around 9.5 when it was assayed by method II, suggesting instability of this myosin under alkaline conditions. In connection with this, the reaction mixture at pH 9.5 showed a very small and slow increase in turbidity, suggesting a change in the physical state of myosin. The ordinary muscle myosin exhibited approximately three times higher actin-activated Mg2+-ATPase activity than the dark muscle myosin. Superprecipitation activity was also higher in the former than the latter actomyosin. However, both actomyosins showed similar pH-superprecipitation activity profiles.
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PMID:The pH-dependency of myosin ATPases from yellowtail ordinary and dark muscles. 623 Dec 79