Calcium- and magnesium-binding properties of a high affinity calcium-binding protein from crayfish sarcoplasm.

نویسندگان

  • W Wnuk
  • J A Cox
  • L G Kohler
  • E A Stein
چکیده

Equilibrium binding studies show that 6 atoms of calcium are bound by the dimeric molecule of the sarcoplasmic calcium-binding protein (SCP) from crayfish. SCP exhibits positive cooperativity in calcium-binding for four sites, as indicated by increasing intrinsic binding constants (1 to 5 x 10” M-l), and negative cooperativity for the other two sites (decreasing constants from 5 to 0.8 x lo7 M-‘). In the presence of 1 mM Mg’+, the binding constants are reduced by about 1 order of magnitude, but cooperativity is conserved. Mg2+ competes with Ca2+ for four out of six sites on SCP. In the absence of Ca’+, magnesium binds to SCP with positive cooperativity for two sites and with negative cooperativity for two others, the four intrinsic binding constants for Mg2+ ranging from 0.4 to 1.0 X 10” M-‘. MgSCP is essentially as stable as Ca-SCP, in contrast to the metal-free protein, which denatures readily. A purified preparation of fragmented sarcoplasmic reticulum removes bound calcium from SCP easily and, in the presence of physiological levels of Mg2+, the latter cation replaces Ca”+ on the Ca-Mg sites, suggesting that exchange of Ca2+ and Mg2’ takes place during muscular activity. With its two calcium-specific sites, two Ca-Mg sites that interact with positive cooperativity and two Ca-Mg sites that interact with negative cooperativity, crayfish SCP displays more complex metal-binding properties than does parvalbumin, the sarcoplasmic calcium-binding protein found in vertebrates which has only two noninteracting Ca-Mg sites. Furthermore, a comparison between the metal-binding properties of SCP’s and troponin C’s from invertebrate muscle reveals that the former are much more complex than the latter. This contrasts sharply with the situation prevailing in vertebrate skeletal muscle, where complexity is found in myofibrillar troponin C and not in sarcoplasmic parvalbumin.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Metal ions binding study on human growth hormone by isothermal titration calorimetric method

The interaction of hGH with some metal ions ( ) at 27°C in NaC1 solution, 50 mM was studied using Isothermal titration calorimetry. There is a set of three identical and non-interacting binding sites for binding of all these metal ions, expect . The intrinsic association equilibrium constants () are not very different for  and , and also their molar enthalpies of binding (KJ/mol for  and  KJ/mo...

متن کامل

Affinity Calcium-binding Protein from Crayfish Sarcoplasm*

The sarcoplasmic calcium-binding protein (SCP) from crayfish has in its dimer form two calcium-specific and four Ca-Mg sites. The conformations of this protein in the calcium(SCP2 *Cas), magnesium(SCP2 -Mg4), and metal-free forms as well as in intermediary states have been studied by circular dichroism (CD) in the far and near-ultraviolet regions, tryptophan fluorescence, sulfhydryl reactivity,...

متن کامل

Properties of the high-affinity single-stranded DNA binding state of the Escherichia coli recA protein.

The properties of the high-affinity single-stranded DNA (ssDNA) binding state of Escherichia coli recA protein have been studied. We find that all of the nucleoside triphosphates that are hydrolyzed by recA protein induce a high-affinity ssDNA binding state. The effect of ATP binding to recA protein was partially separated from the ATP hydrolytic event by substituting calcium chloride for magne...

متن کامل

Calcium binding to extracellular sites of skeletal muscle calcium channels regulates dihydropyridine binding.

The binding of dihydropyridine (PN200-110) to skeletal muscle microsomes (which were 84% sealed inside-out vesicles) was not influenced by the addition of calcium or magnesium nor by addition of their chelators (EDTA or EGTA) unless the vesicles were pretreated with the calcium-magnesium ionophore A23187 and EDTA to remove entrapped cations. Separation of inside-out vesicles from right-side-out...

متن کامل

Properties of passive binding of calcium to endoplasmic reticulum from adipocytes.

Calcium binding to isolated adipocyte microsomes enriched in endoplasmic reticulum has been characterized. Binding was concentration-dependent, saturable, and totally dissociable. Steady state was reached within 20 min at all calcium concentrations tested. Three apparent classes of binding sites were identified in kinetic and steady state studies using calcium concentrations from 1 muM to 10 mM...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:
  • The Journal of biological chemistry

دوره 254 12  شماره 

صفحات  -

تاریخ انتشار 1979