Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chicken gizzard actomyosin, containing the calmodulin-myosin light chain kinase (MLCK) system, was incubated in the presence of various concentrations of PSK, a protein-bound polysaccharide from Basidiomycetes, together with Ca2+ and Mg-ATP. The phosphorylation of myosin was enhanced half-maximally by 10-4 g/ml of PSK. However, a similar concentration of PSK reduced the Mg-ATPase activity of the actomyosin. The former was brought about through stimulation of the MLCK activity and the latter through inhibition of the myosin ATPase activity.
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PMID:A protein-bound polysaccharide from Basidiomycetes enhances myosin phosphorylation but inhibits myosin ATPase activity: studies with a crude actomyosin preparation of chicken gizzard smooth muscle. 183 24

Permeabilized endothelial cell monolayers retracted on exposure to ATP and Ca2+. ADP, inosine triphosphate (ITP), GTP, adenosine 5'-(gamma-thio)triphosphate (ATP-gamma S), and 5'-adenylylimidodiphosphate failed to support retraction. However, ATP gamma S, a substrate for myosin light-chain kinase (MLCK) but not myosin adenosinetriphosphatase (ATPase), combined with ITP, a substrate for myosin ATPase but not MLCK, supported retraction. Two MLCK pseudosubstrate peptides, M5 and SM-1, inhibited endothelial cell retraction equally and more effectively than myosin kinase-inhibitory peptide with a sequence based on the phosphorylated site of myosin light chain. M5 was shown to inhibit thiophosphorylation of endothelial cell myosin light chains. Endothelial cells incubated with exogenous unregulated kinase in the presence of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetra-acetic acid retracted on addition of ATP. This retraction was accompanied by thiophosphorylation of the 19 kDa myosin light chains in the presence of ATP gamma 35S. The N-ethylmaleimide-modified subfragment 1 of myosin heads, a specific inhibitor of actin-myosin interaction, prevented retraction. These data add support to the proposal of a central role for MLCK activation of myosin in endothelial retraction.
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PMID:Regulation of permeabilized endothelial cell retraction by myosin phosphorylation. 185 58

1. Two types of myosins with phosphorylated and dephosphorylated myosin light chains were prepared from Drosophila flies. The former had ATPase (Ca2(+)- and Mg2(+)-activited) activities twice those of the latter. 2. The myosin phosphorylated with crude myosin light chain kinase from flies showed ATPase (Ca2(+)- and Mg2(+)-activated) activaties twice those of the dephosphorylated myosin. 3. It is suggested that phosphorylation of myosin light chains several hours after emergence stimulates myosin ATPase activity so as to facilitate the flight function of the fruitfly.
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PMID:Regulation of Drosophila myosin ATPase activity by phosphorylation of myosin light chains--I. Wild-type fly. 213 97

Isometric force developed by skinned gizzard muscle fiber bundles and levels of phosphorylation and thiophosphorylation of the 20,000-dalton myosin light chain were determined. These data showed a highly non-linear relationship between isometric force and myosin light-chain phosphorylation. Maximum force was developed at approximately 0.2 mol of phosphate/mol of light chain as reported previously (Hoar, P. E., Kerrick, W. G. L., and Cassidy, P. S. (1979) Science 204, 503-506). In contrast, the relationship between isometric force and myosin light-chain thiophosphorylation was linear, with maximum force occurring at 1.0 mol of thiophosphate/mol of myosin light chain. These observations are consistent with the latch-bridge hypothesis for conditions of varying myosin light-chain phosphatase/myosin light-chain kinase activity ratios as discussed by Hai and Murphy [1988) Am. J. Physiol. 254, C99-C106). To further test the latch-bridge hypothesis, ATPase activity was also measured during isometric force development in these fiber bundles. The relationship between isometric force and ATPase activity was linear whether the myosin light chains were phosphorylated or thiophosphorylated. Thus the number of cycling myosin cross-bridges, as measured by ATPase activity, was directly proportional to the force the muscle developed, not to the level of myosin light-chain phosphorylation. This finding that high levels of tension generated at low levels of light-chain phosphorylation are associated with high levels of ATPase activity is inconsistent with the latch-bridge model (Hai and Murphy, 1988).
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PMID:The relationship between ATPase activity, isometric force, and myosin light-chain phosphorylation and thiophosphorylation in skinned smooth muscle fiber bundles from chicken gizzard. 214 Mar 60

Most of the currently available calmodulin (CaM) antagonists inhibit the actions of CaM by binding directly to it. These CaM-binding drugs tend to be relatively nonselective, because they inhibit the interaction of CaM with most, if not all, of its target enzymes. In order to develop more selective CaM antagonists, we synthesized covalent adducts of CaM and several drugs, including chlorpromazine (CPZ), fluphenazine-N-mustard (FNM), and phenoxybenzamine (PBZ), and examined the effects of these adducts on various CaM and Ca2(+)-dependent enzymes. One of the adducts (CPZ-CaM) selectively inhibited the CaM-induced activation of phosphodiesterase and myosin light chain kinase, without affecting the basal activity of either enzyme. The inhibition of these enzymes by CPZ-CaM was competitive with respect to CaM. CPZ-CaM did not inhibit CaM-sensitive Ca2(+)-ATPase or CaM-dependent protein kinase or the CaM-insensitive enzyme protein kinase C. The FNM-CaM and PBZ-CaM adducts did not inhibit the effects of CaM on any of the enzymes, but they selectively activated two of the enzymes; FNM-CaM slightly activated the CaM-dependent protein kinase, and PBZ-CaM slightly activated phosphodiesterase. These results show that certain covalently linked drug-CaM adducts can differentially inhibit or activate various CaM-sensitive enzymes, and they provide further evidence that it may be possible to develop new classes of CaM antagonists that are directed against the CaM recognition sites on CaM-sensitive enzymes.
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PMID:Differential inhibition of calcium-dependent and calmodulin-dependent enzymes by drug-calmodulin adducts. 214 88

Abalone myosin contains two kinds of light chain, regulatory light chain (LC2) and essential light chain (LC1) according to SDS-PAGE. Three distinct light chain bands were observed on polyacrylamide gel electrophoresis of purified abalone myosin in the presence of urea (urea-PAGE). The slower two components showed had mobility on SDS-PAGE and they also showed regulatory activity as the regulatory light chain. They were termed LC2-a and LC2-b in order of increasing mobility on urea-PAGE and isolated by DE-32 ion exchange column chromatography in the presence 8 M urea. The ratio of LC2-a and LC2-b in the central portion of adductor muscle of abalone (LC2-a: LC2-b = 7:3) was different from that (1:1) in the peripheral portion. These results suggest that the two light chains are isoforms of the regulatory light chain. The amino acid compositions of LC2-a and LC2-b were very similar to each other except for the Cys content. The UV absorption spectra were also quite similar, as were the UV difference absorption spectra induced by Ca2+. Phosphorylation was not detectable with the myosin light chain kinase of chicken gizzard. The Ca2+ concentration dependencies of Mg-ATPase activity of LC2-a or LC2-b hybridized abalone myosin (a-myosin, b-myosin) were similar to each other in the absence of rabbit F-actin, but differed in the presence of actin. The b-myosin had a higher maximum value of actomyosin ATPase activity and a lower apparent binding constant of actin and myosin than a-myosin.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Two isoforms of regulatory light chain of abalone smooth muscle myosin. 215 May 17

New heterobifunctional cross-linking reagents that possessed a photoactive terminus, an electrophilic terminus, and a linking arm between the two termini that had a radiolabeled, enzymatically cleavable bond were synthesized. In a model study, succinimidyl N-[N'-(4-azidobenzoyl)tyrosyl]-beta-alanate (16A) was coupled to n-butylamine (a Lys surrogate), iodinated, and cleaved with chymotrypsin in the presence of tyrosylamide to afford the desired adduct (N-(N'-(4-azidobenzoyl)-3-iodotyrosyl)tyrosinamide, thereby demonstrating the feasibility of the enzymatic cleavage. In a biochemical study, succinimidyl N-[N'-(3-azido-5-nitrobenzoyl)tyrosyl]-beta-alanate (16C) was coupled to Lys-75 of calmodulin (CaM), and the radioiodinated monoadduct was successfully photo-cross-linked, in a calcium-dependent manner, to the human erythrocyte plasma membrane Ca2+,Mg2(+)-ATPase and to a synthetic fragment (M13) containing the CaM-binding region of myosin light-chain kinase. In the latter case, densitometry readings indicated 20% cross-linking efficiency.
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PMID:Photoaffinity heterobifunctional cross-linking reagents based on N-(azidobenzoyl)tyrosines. 215 9

Calponin isolated from chicken gizzard smooth muscle inhibits the actin-activated MgATPase activity of smooth muscle myosin in a reconstituted system composed of contractile and regulatory proteins. ATPase inhibition is not due to inhibition of myosin phosphorylation since, at calponin concentrations sufficient to cause maximal ATPase inhibition, myosin phosphorylation was unaffected. Furthermore, calponin inhibited the actin-activated MgATPase of fully phosphorylated or thiophosphorylated myosin. Although calponin is a Ca2(+)-binding protein, inhibition did not require Ca2+. Furthermore, although calponin also binds to tropomyosin, ATPase inhibition was not dependent on the presence of tropomyosin. Calponin was phosphorylated in vitro by protein kinase C and Ca2+/calmodulin-dependent protein kinase II, but not by cAMP- or cGMP-dependent protein kinases, or myosin light chain kinase. Phosphorylation of calponin by either kinase resulted in loss of its ability to inhibit the actomyosin ATPase. The phosphorylated protein retained calmodulin and tropomyosin binding capabilities, but actin binding was greatly reduced. The calponin-actin interaction, therefore, appears to be responsible for inhibition of the actomyosin ATPase. These observations suggest that calponin may be involved in regulating actin-myosin interaction and, therefore, the contractile state of smooth muscle. Calponin function in turn is regulated by Ca2(+)-dependent phosphorylation.
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PMID:Smooth muscle calponin. Inhibition of actomyosin MgATPase and regulation by phosphorylation. 216 34

Brain type II Ca2+/calmodulin-dependent protein kinase was found to phosphorylate smooth muscle myosin, incorporating maximally approximately 2 mol of phosphoryl per mol of myosin, exclusively on the 20,000 dalton light chain subunit. After maximal phosphorylation of myosin or the isolated 20,000 dalton light chain subunit by myosin light chain kinase, the addition of type II Ca2+/calmodulin-dependent protein kinase led to no further incorporation indicating the two kinases phosphorylated a common site. This conclusion was supported by two dimensional mapping of tryptic digests of myosin phosphorylated by the two kinases. By phosphoamino acid analysis the phosphorylated residue was identified as a serine. The phosphorylation by type II Ca2+/calmodulin-dependent protein kinase of myosin resulted in enhancement of its actin-activated Mg2(+)-ATPase activity. Taken together, these data strongly support the conclusion that type II Ca2+/calmodulin-dependent protein kinase phosphorylates the same amino acid residue on the 20,000 dalton light chain subunit of smooth muscle myosin as is phosphorylated by myosin light chain kinase and suggest an alternative mechanism for the regulation of actin-myosin interaction.
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PMID:Phosphorylation of smooth muscle myosin by type II Ca2+/calmodulin-dependent protein kinase. 217 1

Contractile activity of the smooth muscle cell is regulated by the concentration of intracellular Ca2+. The Ca2+ transients are sensed by the target protein, calmodulin, and via activation of myosin light chain kinase (by Ca2(+)-calmodulin) transmitted to the contractile apparatus. Phosphorylation of myosin increases its actin-activated ATPase activity and in smooth muscle fibers is thought to initiate contraction. The effects of phosphorylation on the conformation of myosin are not established, but at least two areas of the molecule are influenced by phosphorylation of the two light chains. These are at the actin-binding site and at the head-neck junction. The latter site is important in regulating ATPase activity and a working hypothesis is that phosphorylation increases flexibility at this site and facilitates cross-bridge cycling. The phosphorylation theory has extensive experimental support, and is accepted as a major regulatory component in smooth muscle. However, the simplest interpretation of this scheme cannot adequately account for the varied physiological responses. Either there are aspects of the phosphorylation theory that are not considered, or an additional regulatory mechanism is involved. Both possibilities are discussed.
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PMID:Phosphorylation of myosin as a regulatory mechanism in smooth muscle. 218 76


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