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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

As previously reported, rho-nitrobenzenediazonium fluoroborate strongly inhibits Ca2+- ATPase of myosin [EC 3.6.1.3] without appreciable suppression of its EDTA-K+- ATPase activity, and the presence of ATP in the reaction medium reverses the pattern of alteration in both ATPase activities, i.e., causing selective inhibition of EDTA-K+ -ATPase. Spectrophotometric studies on the azo-coupling products of 17 amino acids and their derivatives revealed that the amino acid residue of myosin modified by the diazonium dye was cysteine in both the presence and absence of ATP. It is also suggested that the number of cysteinyl residues responsible for the activity changes was one mole per mole of myosin subunit.
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PMID:Thiols of myosin. III. Spectrophotometric identification of the amino acid residue of myosin modified by rho-nitrobenzenediazonium fluoroborate. 13 31

The initial burst of Pi liberation during the hydrolysis of Mn(II)-ATP by heavy meromyosin from rabbit psoas muscle was investigated. Below 10 degrees, the initial burst of Pi liberation was inhibited by the pre-addition of ADP without any change in the steady-state activity, but it was not inhibited above 10 degrees. The burst size was about one mole per mole of heavy meromyosin. The initial burst of Pi liberation in Mg-ATP hydrolysis at 8 degrees, however, was not inhibited by the pre-addition of ADP. These results, obtained with psoas muscle heavy meromyosin, were almost the same as those obtained with heavy meromyosin from rabbit leg and back muscles (Hozumi and Tawada (1975) Biochim. Biophys. Acta 376, 1-12) and, therefore, indicate that in Mn-ATP above 10 degrees there is at the burst site a predominant myosin -product complex generated by ATP hydrolysis. Similarly, below 10 degrees there is a myosin-product complex identical with the one generated by adding ADP (and Pi) to myosin.
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PMID:Temperature-dependent transitions of the myosin-product intermediate at 10 degrees during Mn(II)-ATP hydrolysis by myosin from rabbit psoas muscle. 13 32

A calorimetric titration method was used to study ADP binding to native myosin. Data were analyzed by assuming that the myosin molecule has n independent and identical sites for ADP binding. The enthalpy change (deltaH), the binding constant (K), and n were determined. In 0.5 M KCl, 0.01 M MgCl2, and 0.02 M Tris/HCl (pH 7.8), we found: at 0 degrees, deltaH = -57.1 +/- 3.2 kJ-mol-1, log K = 6.42 +/- 0.13, n = 1.49 +/- 0.07; at 12 degrees, deltaH = 73.1 +/- 3.2 kJ-mole-1, log K = 6.08 +/- 0.13, and n = 1.74 +/- 0.07. The average heat capacity change on ADP binding to myosin between 0 and 12 degrees is thus -1.4 +/- 0.4 kJ-mol-1-K-1. Reasonably consistent results were obtained at 25 degrees, suggesting ADP binding to myosin is as strongly exothermic as at lower temperatures, although further interpretation of this result seems unwarranted, mainly because of the instability of myosic at this temperature. The number of protons released on binding of ADP to myosin was determined in separate experiments. The value was 0.19 +/- 0.02 at both 0 and 12 degrees. The reaction of protons with Tris thus contributes about -9.5 kJ-mol-1 to the observed heat on ADP binding.
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PMID:Calorimetric studies of the interaction of myosin with ADP. 13 38

1. The myosin content of myofibrils was found to be 51% by SDS-gel electrophoresis. 2. The initial burst of Pi liberation of the ATPase [EC 3.6.1.3] of a solution of myofibrils in 1 M KCl was measured in 0.5 M KCl, and found to be 0.93 mole/mole of myosin. 3. The amount of ADP bound to myofibrils during the ATPase reaction and the ATPase activity were measured by coupling the myofibrillar ATPase reaction with sufficient amounts of pyruvate kinase [EC 2.7.1.40] and PEP to regenerate ATP. The maximum amount of ADP bound to myofibrils in 0.05M KCl and in the relaxed state was about 1.5 mole/mole of myosin. On the other hand, the ATPase activity exhibited substrate inhibition, and the amount of ATP required for a constant level of ATPase activity was smaller than that required for the maximum binding of ADP to myofibrils. 4. The maximum amount of ADP bound to myofibrils in 0.5 M KCl was about 1.9 mole/mole of myosin. When about one mole of ADP was found to 1 mole of myosin in myofibrils, the myofibrillar ATPase activity reached the saturated level, and with further increase in the concentration of ATP one more mole of ADP was found per mole of myosin.
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PMID:Structure and function of the two heads of the myosin molecule. I. Binding of adenosine diphosphate to myofibrils during the adenosinetriphosphatase reaction. 13 77

Subfragment-1 of HMM was prepared by tryptic [EC 3.4.21.4] digestion of HMM, which had been modified with 1 mole of CMB per mole of HMM at a specific SH group, SHr. S-1(T) obtained from CMB-HMM retained almost all the CMB, and the amount of bound CMB was about 0.8-0.9 mole per 2 moles of S-1(T). S-2 of CMB-HMM contained no bound CMB. The ATPase [EC 3.6.1.3] activity of HMM increased gradually with increase in the concentration of FA, and the acto-HMM ATPase was inhibited by excess substrate or removal of Ca2+ ions in the presence of RP. The ATPase activity of CMB-HMM increased to a maximum level on adding a small amount of FA, and the acto-CMB-HMM ATPase showed neither substrate inhibition nor Ca2+ sensitivity in the presence of RP. On the other hand, the dependence on the concentration of FA of the ATPase activity of acto-S-1(T) was unaffected by modification of S-1 with CMB. The Ca2+ sensitivity of the ATPase activity of acto-S-1(T) in the presence of RP was also unaffected by the modification. Acto-S-1(T) dissociated almost completely, while acto-CMB-S-1(T) was only 50% dissociated on adding ATP. More than 80% of the bound CMB was contained in S-1(T) undissociated from FA. Furthermore, superprecipitation of actomyosin induced by ATP was completely inhibited by adding about 2 moles of CMB-S-1(T) per mole of actin monomer. On the other hand, about 90% of the burst size of Pi liberation was retained in S-1(T) dissociated from FA. It was concluded that the two heads of the myosin molecule are different: one shows the initial burst of Pi liberation, and does not contain the SHr group which binds CMB (head B), and the other does not show the initial burst and contains the SHr group (head A). It was also concluded that modification of head A of HMM or myosin with CMB increases its binding strength to FA, and consequently the substrate inhibition and Ca2+ sensitivity of acto-HMM or actomyosin ATPase at head B are lost on modification of head A with CMB. CMB-S-1(CT) was prepared by chymotryptic [EC 3.4.21.1] digestion of CMB-myosin, and separated into two fractions by ultracentrifugation of acto-CMB-S-1(CT) in the presence of ATP. Three components of CMB-S-1(CT) with molecular weights of 9, 2.4, and 1.2 X 10(4) were separated by SDS-polyacrylamide gel electrophoresis. The ratios of the peak areas of the three components in electrophoretograms were the same in CMB-S-1(CT) and in the two fractions (1 : 0.18 : 0.09), indicating that heads A and B have the same subunit structure.
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PMID:Structure and function of the two heads of the myosin molecule. III. Cooperativity of the two heads of the myosin molecule, shown by the effect of modification of head A with rho-chloromercuribenzoate on the interaction of head B with F-actin. 13 79

The P light chain of cardiac myosin is phosphorylated and dephosphorylated by highly specific enzymes. These reactions take place in the beating rabbit heart and there is evidence that dephosphorylation of the light chain occurs during the inotropic response produced by adrenaline. The extent of phosphorylation of cardiac troponin I is determined by the functional state of the beating heart. During perfusion of the rabbit heart the basal phosphate content of troponin I increased from the basal level of about 1.5 moles P per mole to about 2.7 moles P per mole at the height of the inotropic response to adrenaline. The three sites of phosphorylation on troponin I are probably located in the N terminal cyanogen bromide peptide of 48 residues.
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PMID:Phosphorylation of cardiac myofibrillar proteins. 14 26

The maximal ATP-induced enhancement of fluorescence and the dependence of this enhancement on ATP concentration were determined for myosins from fast and slow skeletal and cardiac muscle of the rabbit. With myosins from slow and cardiac muscle modifications in the preparative procedure and chromatography on DEAE-Sephadex were required to obtain preprations which were free of actin, which exhibited the maximal fluorescence enhancement and which bound two moles of ATP per mole of myosin. Since the fluorescence enhancement of cardiac and slow muscle myosins is labile at slightly alkaline pH, it was also necessary to minimize incubation at pH greater than 7 in order to attain the maximal enhancement. With fast muscle myosin the changes in preparative procedure, together with chromatography, led to a 50 to 100% increase in the steady-state rate of ATP hydrolysis and fluorescence enhancement, without changing the maximal binding of ATP. From a comparison of the rate of steady-state hydrolysis of ATP with the rate of decay of the enhanced fluorescence, it appears that for all three myosins, both ATP binding sites have the same enzymatic activity, the steady-state rate per site being slower for cardiac and slow muscle myosins than for fast muscle myosin.
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PMID:Enzymatic activities and ATP-induced fluorescence enhancement of myosin from fast and slow skeletal and cardiac muscles. 15 60

1. Binding of MG-ADP to both heart and fast skeletal myosin was found with 3 methods to proceed in 2 steps. One mole of MG-ADP binds with high affinity (K approximately equal to 10(6) M-1) and subsequently a second with lower affinity (K approximately equal to 10(2)-10(4) M-1) per myosin. Only one mole of MG-ADP was found to bind with the high affinity to isolated myosin heads. This implies that binding of MG-ADP to intact myosin exhibits negative cooperativity. 2. When a nucleotide is bound, the 2 heads of a single myosin molecule adopt different conformations since on each head a different type of essential thiol group was found to be the most reactive towards N-ethylmaleimide. In the presence of MG-pyrophosphate a thiol-1 is the most reactive essential group in both heads. Therefore, the nucleoside moiety seems to be required for this latter type of head-head interaction.
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PMID:Evidence for head-head interactions in myosin from cardiac and skeletal muscles. 19 85

The M-line protein which is identical to the muscle form of creatine kinase was purified from rabbit skeletal muscle using ion exchange chromatography. Gel electrophoresis in the presence and absence of sodium dodecyl sulfate revealed the protein to be homogeneous. Sodium dodecyl sulfate gel electrophoresis gave 44 000 +/- 2000 as the minimum molecular weight while low speed sedimentation equilibrium experiments yielded a molecular weight of 84 000 +/- 4000, suggesting that the parent molecule is a dimer. Circular dichroism spectra revealed the presence of two negative dichroic bands located at 218 and 208 nm suggesting the presence of some beta-structure. Ellipticity values at these two wavelengths were -8000 +/- 400 and -9000 +/- 400 deg-cm2-dmol-1. Circular dichroism measurements indicated the protein to interact with myosin, heavy meromyosin and heavy meromyosin subfragment 1 (S1). The Ca2+-activated ATPase activities of myosin, heavy meromyosin and subfragment 1 were inhibited by the addition of M-line protein. When the protein was mixed with subfragment 1 in a 1:1 mole ratio in 0.15 M KC1, 50 mM Tris pH 8, low speed sedimentation equilibrium studies gave a molecular weight of 205 000 +/- 10 000 for the complex, indicative of an interaction of the two components. Both circular dichroism and sedimentation equilibrium studies indicated no interaction of M-line protein with light meromyosin.
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PMID:Physicochemical studies on the creatine kinase M-line protein and its interaction with myosin and myosin fragments. 79 21

Light chains of skeletal muscle myosin were studied through the reactivity of their SH groups with a fluorescent thiol reagent, N-(7-dimethylamino-4-methylcoumarinyl) maleimide (DACM). The experiments were carried out by reacting the reagent with myosin for a short time and measuring the amounts of reacted dye by fluorometry after separating light chains by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The two classes of light chains, alkali light chains and DTNB light chain, were clearly distinguished by their manner of reactivity change, and differences in their environment and in their function were suggested. Although we found that the SH groups of the DTNB light chain were susceptible to very low concentrations of Mg ions (of the order of 10-5 M), we could not observe Ca2+-induced conformational change by our technique. We also estimated the stoichiometry of light chains in skeletal muscle myosin to be 1.37 mol alkali light chain 1, 1.95 mol of DTNB light chain and 0.77 mol of alkali light chain 2 per mole of myosin from the total amounts of our reagent that reacted with each light chain.
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PMID:Fluorometric studies on the light chains of skeletal muscle myosin. I. Effects of temperature, ionic strength, divalent metal ions, and nucleotides. 91 9


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