%0 Journal Article %1 Robe_1981_559 %A Robertson, S. P. %A Johnson, J. D. %A Potter, J. D. %D 1981 %J Biophys. J. %K 7195747 Activation, Animals, Binding Binding, Biological, Calcium, Calcium-Binding Calmodulin, Competitive, Computers, Contraction, Cytoskeleton, Enzyme Gov't, Humans, Kinetics, Magnesium, Models, Muscle Muscles, Myosins, Non-U.S. P.H.S., Parvalbumins, Proteins, Research Sites, Support, Troponin, U.S. %N 3 %P 559--569 %T The time-course of Ca$^2+$ exchange with calmodulin, troponin, parvalbumin, and myosin in response to transient increases in Ca$^2+$. %U http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7195747&query_hl=37 %V 34 %X We have modeled the time-course of Ca$^2+$ binding to calmodulin, troponin, parvalbumin, and myosin in response to trains of transient increases in the free myoplasmic calcium ion concentration (pCa). A simple mathematical expression was used to describe each pCa transient, the shape and duration of which is qualitatively similar to those thought to occur in vivo. These calculations assumed that all individual metal binding sites are noninteracting and that Ca$^2+$ bind competitively to the Ca$^2+$-Mg2+ sites of troponin, parvalbumin, and myosin. All the on-and-off rate constants for both Ca$^2+$ and Mg2+ were obtained either from the literature or from our own research. The percent saturation of the Ca$^2+$-Mg2+ sites with Ca$^2+$ was found to change very little in response to each pCa transient in the presence of 2.5 X 10(-3)M Mg2+. Our analysis suggests that the Ca$^2+$ content of these sites is a measure of the intensity and frequency of recent muscle activity because large changes in the Ca$^2+$ occupancy of these sites can occur with repeated stimulation. In contrast, large rapid changes in the amount of Ca$^2+$ bound to the Ca$^2+$-specific sites of troponin and calmodulin are induced by each pCa transient. Thus, only sites of the "Ca$^2+$-specific" type can act as rapid Ca$^2+$-regulatory sites in muscle. Fluctuation in the total amount of Ca$^2+$ bound to these sites in response to various types of pCa transients further suggests that in vivo only about one-half to one-third of the total steady-state myofibrillar Ca$^2+$-binding capacity exchanges Ca$^2+$ during any single transient.

@article{Robe_1981_559, abstract = {We have modeled the time-course of {C}a$^{2+}$ binding to calmodulin, troponin, parvalbumin, and myosin in response to trains of transient increases in the free myoplasmic calcium ion concentration (pCa). A simple mathematical expression was used to describe each pCa transient, the shape and duration of which is qualitatively similar to those thought to occur in vivo. These calculations assumed that all individual metal binding sites are noninteracting and that {C}a$^{2+}$ bind competitively to the {C}a$^{2+}$-Mg2+ sites of troponin, parvalbumin, and myosin. All the on-and-off rate constants for both {C}a$^{2+}$ and Mg2+ were obtained either from the literature or from our own research. The percent saturation of the {C}a$^{2+}$-Mg2+ sites with {C}a$^{2+}$ was found to change very little in response to each pCa transient in the presence of 2.5 {X} 10(-3)M Mg2+. Our analysis suggests that the {C}a$^{2+}$ content of these sites is a measure of the intensity and frequency of recent muscle activity because large changes in the {C}a$^{2+}$ occupancy of these sites can occur with repeated stimulation. In contrast, large rapid changes in the amount of {C}a$^{2+}$ bound to the {C}a$^{2+}$-specific sites of troponin and calmodulin are induced by each pCa transient. Thus, only sites of the "{C}a$^{2+}$-specific" type can act as rapid {C}a$^{2+}$-regulatory sites in muscle. Fluctuation in the total amount of {C}a$^{2+}$ bound to these sites in response to various types of pCa transients further suggests that in vivo only about one-half to one-third of the total steady-state myofibrillar {C}a$^{2+}$-binding capacity exchanges {C}a$^{2+}$ during any single transient.}, added-at = {2009-06-03T11:20:58.000+0200}, author = {Robertson, S. P. and Johnson, J. D. and Potter, J. D.}, biburl = {https://www.bibsonomy.org/bibtex/29dbebdd39b41ad6c0503068875903947/hake}, description = {The whole bibliography file I use.}, interhash = {9a76f3f8e1c670c0566b6316a02d3edf}, intrahash = {9dbebdd39b41ad6c0503068875903947}, journal = {Biophys. J.}, key = 88, keywords = {7195747 Activation, Animals, Binding Binding, Biological, Calcium, Calcium-Binding Calmodulin, Competitive, Computers, Contraction, Cytoskeleton, Enzyme Gov't, Humans, Kinetics, Magnesium, Models, Muscle Muscles, Myosins, Non-U.S. P.H.S., Parvalbumins, Proteins, Research Sites, Support, Troponin, U.S.}, month = Jun, number = 3, pages = {559--569}, pmid = {7195747}, timestamp = {2009-06-03T11:21:27.000+0200}, title = {The time-course of {C}a$^{2+}$ exchange with calmodulin, troponin, parvalbumin, and myosin in response to transient increases in {C}a$^{2+}$.}, url = {http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7195747&query_hl=37}, volume = 34, year = 1981 }