+ Resolve Article
+ Follow Us
Follow on FacebookFollow on Facebook
Follow on TwitterFollow on Twitter

+ Translate
+ Subscribe to Site Feed
GeoScience Most Shared ContentMost Shared Content

Sequential mechanism of calcium binding and translocation in sarcoplasmic reticulum atpase

, : Sequential mechanism of calcium binding and translocation in sarcoplasmic reticulum atpase. Journal of Biological Chemistry 262(34): 16338-16342

Cooperative calcium binding (apparent Kd = 1.04 .times. 10-6 M) to the ATPase of sarcoplasmic reticulum vesicles occurs with a maximal stoichiometry of 2 mols of divalent cation/mol of enzyme in the absence of ATP. The bound calcium is distributed into two pools which undergo fast or slow isotopic exchange, respectively. The two pools retain a 1:1 molar ratio under various conditions and are both located within a protein crevice, as suggested by their cooperative interaction and exchange kinetics. Following enzyme phosphorylation by ATP, both pools of bound calcium are "internalized" (cannot be displaced by quench reagents). If following 45Ca2+ binding, isotopic dilution is obtained in the medium by adding 40Ca2+ with ATP, internalization of both pools of bound 45Ca2+ (2 mol/mol of phosphoenzyme) is still observed within the first enzyme cycle. When the cycle is reversed by addition of excess ADP soon after ATP, only half of the internalized 45Ca2+ is released from the enzyme into the medium outside the vesicles, while the other half remains with the vesicles. If half of the bound 45Ca2+ is exchanged (fast exchange) with 40Ca2+ previous to the addition of ATP, none of the remaining 45Ca2+ is released outside the vesicles upon reversal of the enzyme cycle. Therefore, the pool of bound calcium which undergoes slower exchange with the outside medium, is the first to be released inside the vesicles upon enzyme phosphorylation. A sequential mechanism of calcium binding and translocation is proposed, that accounts for binding cooperativity and exchange kinetics, presteady state transients following addition of ATP, and the Ca2+ concentration dependence of ATPase activity in steady state.


Other references

Venier, L.A.; Mckenney, D.W.; Wang, Y.; Mckee, J.E., 1997: Distribution of breeding birds in relation to climate in Ontario, Canada. Bulletin of the Ecological Society of America 78(4 SUPPL ): 201

Henderson, A.; Vist, G.; Rumsey, D., 1998: The effect of a three week high fat diet on the mouth to caecum transit time of a high fat meal in humans. Biochemical Society Transactions 26(2): S186-S186

Shimomura, M.; Mawatari, S.F., 2000: Two new species of Munnogonium (Isopoda: Asellota: Paramunnidae) from Japan. Species Diversity. August; 53: 215-227

Jacobsen, M.; Detjen, A.K.; Mueller, H.; Gutschmidt, A.; Leitner, S.; Wahn, U.; Magdorf, K.; Kaufmann, S.H.E., 2007: Clonal expansion of CD8+ effector T cells in childhood tuberculosis. The role of CD8(+) T cells in human tuberculosis (TB) remains elusive. We analyzed the T cell repertoire and phenotype in 1) children with active TB (< or =4 years), 2) healthy latently Mycobacterium tuberculosis-infected children, and 3) nonin...

Refaat, B.; Amer, S.; Ola, B.; Chapman, N.; Ledger, W., 2008: The expression of activin-beta A- and -beta B-subunits, follistatin, and activin type 11 receptors in fallopian tubes bearing an ectopic pregnancy. Context: Ectopic pregnancy is a major cause of maternal morbidity and mortality with increasing incidence worldwide.Objective: We investigated whether epithelia from Fallopian tubes (FTs) bearing an ectopic pregnancy differ from normal tubes in ex...

Osheroff, N.; Borden, D.; Koppenol, W.H.; Margoliash, E., 1980: Electrostatic interactions in cytochrome c. The role of interactions between residues 13 and 90 and residues 79 and 47 in stabilizing the heme crevice structure. Stability of the native conformation of the heme crevice of ferricytochrome c, as assessed by the pK.alpha. and transition temperature (t1/2) values for the 695 nm absorption band, varies considerably among native and singly modified proteins of m...

Ivankovic, S., 1978: Gastric cancer in rats after chronic intraperitoneal applicaion of sap of green parts of potatoes (Solanum tuberosum L.). Experientia 34 (5) 645

Zatorre R.J., 1979: Recognition of dich otic melodies by musicians and nonmusicians. A dichotic recognition test was administered to 24 musicians and 24 nonmusicians. The stimuli consisted of melodic, random diatonic and random chromatic melodies (previously rated as to melodic content) and speech syllables. Left ear advantages we...

Foy C.F., 1986: Symposium on interferons as cell growth inhibitors and antitumor factors held at the 15th annual meeting of the ucla university of california los angeles symposia on molecular and cellular biology april 6 12 1986. Journal of Cellular Biochemistry Supplement (10 PART C): 215-248

Smith, E.B.; Bartruff, J.K.; Blanchard, V., 1970: Skin biopsy in cases of secondary syphilis. British Journal of Venereal Diseases 46(5): 426-426