Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “HMM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources
PubMed1987

Binding of phosphorylated and dephosphorylated heavy meromyosin to F-actin.

The effect of myosin light chain phosphorylation in skeletal muscle was investigated with respect to the binding affinity of phosphorylated and dephosphorylated heavy meromyosin (HMM) for F-actin in the absence of ATP. For phosphorylated HMM the affinity was 2.5-times weaker in the presence of Ca2+ as in its absence (HMM divalent binding sites saturated only with Mg). For dephosphorylated HMM the reverse was true, the binding being 2.4-times higher in the presence of Ca2+.

Actins↗
PubMed1988

Aorta caldesmon inhibits actin activation of thiophosphorylated heavy meromyosin Mg2+-ATPase activity by slowing the rate of product release.

Activation of aorta thiophosphorylated heavy meromyosin (HMM[SP]) Mg2+-ATPase activity by aorta actin and the fraction of HMM[SP]-substrate intermediate complexes bound to actin were measured simultaneously. At 25 degrees C the Km for ATPase activation and the dissociation constant for the binding reaction were similar, irrespective of the presence or absence of tropomyosin. Aorta caldesmon (0.1 mol/mol actin) inhibited ATPase activation by 80-90% but did not alter the binding of HMM[SP]-product intermediates to actin. It is concluded that caldesmon inhibits by slowing the rate-limiting release of products from the actin-HMM[SP].ADP.Pi complex.

Actins↗
PubMed1986

Phosphorylation in skeletal myosin light chain modulates the actin--myosin interaction in the presence of regulatory proteins in vitro.

The effect of phosphorylation in skeletal myosin light chain (LC2) on the actomyosin and acto-heavymeromyosin (HMM) ATPase activities was investigated in the presence or absence of regulatory proteins (tropomyosin-troponin complex). Phosphorylation in LC2 did not modulate the actin-myosin and actin-HMM interactions over a wide range of KCl concentrations from 30 to 150 mM without regulatory proteins. In the presence of regulatory proteins, phosphorylation in myosin LC2 enhanced the ATPase activity of actomyosin with calcium ions, but the removal of calcium ions made little difference in the ATPase activity between phosphorylated and dephosphorylated myosins. Ca2+-sensitivity of the regulated actomyosin was slightly changed by phosphorylation in myosin LC2. However, both the ATPase activity and Ca2+-sensitivity of the regulated acto-HMM were unaffected by phosphorylation in HMM LC2.

Actins↗
PubMed1994

Selective uptake of high-density lipoprotein-associated cholesteryl esters and high-density lipoprotein particle uptake by human monocyte-macrophages.

High-density lipoprotein (HDL) cholesteryl esters (CE) are taken up by many cells without parallel uptake of HDL apolipoproteins. This selective uptake of HDL CE was investigated in human monocyte-derived macrophages (HMM). HDL3 (d = 1.125-1.21 g/ml) was labeled in its apolipoprotein A-I moiety with 125I and in its CE moiety with [3H]cholesteryl oleyl ether. Cultured human monocyte-macrophages were incubated in the presence of doubly labeled HDL3 followed by determination of tracer uptake. HMM took up HDL3 particles as indicated by the uptake of HDL3 apolipoproteins. Uptake of HDL3-associated CE tracer was in significant excess of that due to HDL3 particle uptake indicating selective uptake of CE. Increased cell cholesterol due to preincubation with acetylated low-density lipoprotein (LDL) down-regulated selective uptake by HMM. According to several experimental approaches, selective uptake of HDL3 CE was independent from cell-secreted products, LDL receptor-mediated endocytosis or HDL3 retroendocytosis. The intracellular catabolism of HDL3 CE was investigated with HDL3 labeled in its CE moiety with [3H]cholesteryl oleate. The lysosomal inhibitor chloroquine had no effect on CE hydrolysis indicating that CE selectively taken up is hydrolyzed independently from lysosomes. In conclusion, HMM selectively take up HDL3-associated CE. The cellular mechanism of selective uptake is independent from endocytosis or retroendocytosis. Intracellularly, HDL3 CE selectively taken up are catabolized independently from lysosomes.

Apolipoprotein A-I↗
PubMed1984

X-ray scattering by single-headed heavy meromyosin. Cleavage of the myosin head from the rod does not change its shape.

Low angle X-ray scattering from heavy meromyosin (HMM) and from single-headed heavy meromyosin (sHMM) have been examined to determine if the heads of myosin change shape when cleaved from the rod to form subfragment 1 (S1). The scattering intensities of intact HMM and sHMM were compared with those of their chymotryptic digestion products, S1 and subfragment 2 (S2). As the data with HMM were complicated by scattering between the two heads, the more extensive analysis was done with sHMM. Pseudo-Guinier plots of intact and digested sHMM, over the angular range used previously for S1, were linear and showed a difference in apparent radius of gyration (Rg) of only 0.07 +/- 0.04 nm. The absolute apparent Rg value of sHMM was 3.2 +/- 0.2 nm, which is comparable to the radius of gyration reported previously for S1 alone. A plot of the fractional differences in scattering intensities of intact and digested sHMM was flat to a reciprocal spacing of at least 1/3.5 nm-1. These results indicate that the head portions of sHMM and S1 have very similar structures at low resolution. Scattering curves for various models of sHMM and mixtures of S1 and S2 were calculated and the fractional difference plots of scattering intensities were made to determine how sensitive this type of analysis is to changes in the shape of the head. Changes in Rg of 0.1 nm or greater gave detectably non-flat difference plots. Thus, the X-ray scattering of sHMM (and HMM) demonstrated that differences in structure between the head of myosin and isolated S1 are likely to be small. Current controversies over myosin head structure are discussed in light of this result.

Animals↗
PubMed1990

Orientation of spin-labeled light chain 2 of myosin heads in muscle fibers.

Electron paramagnetic resonance (e.p.r.) spectroscopy has been used to monitor the orientation of spin labels attached rigidly to a reactive SH residue on the light chain 2 (LC2) of myosin heads in muscle fibers. e.p.r. spectra from spin-labeled myosin subfragment-1 (S1), allowed to diffuse into unlabeled rigor (ATP-free) fibers, were roughly approximated by a narrow angular distribution of spin labels centered at 66 degrees relative to the fiber axis, indicating a uniform orientation of S1 bound to actin. On the other hand, spectra from spin-labeled heavy meromyosin (HMM) were roughly approximated by two narrow angular distributions centered at 42 degrees and 66 degrees, suggesting that the LC2 domains of the two HMM heads have different orientations. In contrast to S1 or HMM, the spectra from rigor fibers, in which LC2 of endogenous myosin heads was labeled, showed a random orientation which may be due to distortion imposed by the structure of the filament lattice and the mismatch of the helical periodicities of the thick and thin filaments. However, spectra from the fibers in the presence of ATP analog 5'-adenylyl imidodiphosphate (AMPPNP) were approximated by two narrow angular distributions similar to those obtained with HMM. Thus, AMPPNP may cause the LC2 domain to be less flexible and/or the S2 portion to be more flexible, so as to release the distortion of the LC2 domain and make it return to its natural position. At high ionic strength, AMPPNP disoriented the spin labels as ATP did under relaxing conditions, suggesting that the myosin head is detached from and/or weakly (flexibly) attached to a thin filament.

Adenosine Triphosphate↗
PubMed1991

Mechanism of the active movement of actin: is actin sliding directly or indirectly related to binding with myosin and activation of myosin ATPase?

In the present work we examined the effect of crosslinking of polymerized and monomeric actin with glutaraldehyde, EDC and DSS on: 1) binding of actin to HMM in solution; 2) activation of HMM ATPase; 3) sliding movement of actin on glass-attached myosin; 4) properties of actin itself, like polymerizability and exchangeability of tightly bound nucleotide. The obtained data show that inhibition of sliding cannot be explained only by changes in the extent of activation of HMM ATPase and binding of actin to HMM; this result emphasizes the role of structural properties of actin in the mechanism of movement generation.

Actins↗
PubMed1990

Translational motion of actin filaments in the presence of heavy meromyosin and MgATP as measured by Doppler broadening of laser light scattering.

Intensity fluctuations of laser light scattering were utilized in order to follow enhancement of translational motion of the actin-heavy meromyosin (HMM) complex in extremely dilute solutions accompanied by the hydrolysis of MgATP. Such enhancement was anticipated on the basis of the idea that active streaming along actin filaments should be associated with their mechanochemical reactivity. Native tropomyosin was added in order to stabilize actin in its filamentous form, thus allowing the reduction of actin concentration below 50 micrograms/ml to enable free movement of neighboring filaments and yet give a reliable signal. Analysis of the data in terms of Doppler broadening led to an approximate evaluation of the average velocity of translation of the mobile filaments. This velocity was found to increase with increasing HMM concentration up to a maximum attained at a molar ratio HMM/actin of 1:2, and then decreased. Total intensity measurements indicate that the mobile scatterer is actually a complex of HMM with an isolated actin filament. HMM subfragment-1 was found to be ineffective. These results suggest that cooperation between the two myosin heads is necessary for efficient induction of active streaming along isolated actin filaments.

Actins↗
PubMed1982

cis-Dichlorodiammineplatinum (II) and hexamethylmelamine in advanced ovarian carcinoma: a phase II study.

Thirty-eight previously treated patients with ovarian carcinoma received a combination of cis-dichlorodiammineplatinum (II) (CDDP) and hexamethylmelamine (HMM). The schedule was CDDP 75 mg/m2 i.v. with forced diuresis on day 1, followed by HMM 200 mg/m2 p.o. on days 8-21, repeated every 4 weeks. In 29 evaluable patients an overall response rate (CR + PR) of 35% with a median response duration of 4.5 months was observed. The performance status seemed to be an important prognostic factor. The gastrointestinal- and neurotoxicities were severe and resulted in dose modification and/or drug discontinuation in half of the patients. In conclusion, CDDP and HMM is an active drug combination in advanced ovarian carcinoma resistant to conventional chemotherapy. A possible superiority of this combination compared with CDDP or HMM alone has to await randomized trials.

Adult↗
PubMed1989

Calcium binding and calcium-sensitivity of heavy meromyosin and subfragment-1 from squid (Todarodes pacificus) mantle and scallop (Patinopecten yessoensis) adductor muscles.

1. HMM and S-1 both bind one mol of calcium per mole of head, and a half of the calcium binding was diminished upon magnesium addition (10 mM) at the low affinity site. 2. The Mg-ATPase activity of HMM (without actin) was fully activated by the binding of one mol of calcium bound per mol of HMM. 3. The calcium binding profile to S-1 is the same as that to HMM, however, the Mg-ATPase activity of S-1 is independent of calcium binding. It is suggested that there are two kinds of myosin head (or S-1) in molluscan myosin, functionally different in calcium binding properties.

Animals↗
PubMed2006

Sequence-based protein structure prediction using a reduced state-space hidden Markov model.

This work describes the use of a hidden Markov model (HMM), with a reduced number of states, which simultaneously learns amino acid sequence and secondary structure for proteins of known three-dimensional structure and it is used for two tasks: protein class prediction and fold recognition. The Protein Data Bank and the annotation of the SCOP database are used for training and evaluation of the proposed HMM for a number of protein classes and folds. Results demonstrate that the reduced state-space HMM performs equivalently, or even better in some cases, on classifying proteins than a HMM trained with the amino acid sequence. The major advantage of the proposed approach is that a small number of states is employed and the training algorithm is of low complexity and thus relatively fast.

Algorithms↗
PubMed1995

Mode of caldesmon binding to smooth muscle thin filament: possible projection of the amino-terminal of caldesmon from native thin filament.

The structure of smooth muscle thin filament was examined by various electron microscopy techniques, with special attention to the mode of caldesmon binding. Chemical cross-linking was positively used to avoid the dissociation of accessory proteins upon dilution. Caldesmon in reconstituted thin filament was observed as fine filamentous projections from thin filament. Native thin filament isolated from smooth muscle showed similarly numerous fine whisker-like projections by all the techniques employed here. Antibody against the amino-terminus of caldesmon labeled the end of such projections indicating the possibility that the amino-terminal myosin binding moiety might stick out from the shaft of the thin filament. Such whiskers are often projected out as a cluster to the same side of native thin filament. Further, we could visualize the assembly of dephosphorylated heavy meromyosin (HMM) with native or reconstituted thin filament forming "nonproductive" complex in the presence of ATP. The association of HMM to the shaft of thin filament was through subfragment-2 moiety, in accordance with biochemical studies. Some HMM particles bound closer to the thin filament shaft, possibly suggesting the presence of the second myosin-binding site on caldesmon. Occasionally two kinds of HMM association as such coexisted at a single site on this filament in tandem. Thus, we constructed a structural model of thin filament. The proposed molecular arrangement is not only compatible with all the biochemical results but also provides additional support for our recent findings (E. Katayoma, G. C. Scott-Woo, and M. Ikebe (1995) J. Biol. Chem. 270, 3919-3925) regarding the capability of caldesmon to induce dephosphorylated myosin filament, which explains the existence of thick filaments in relaxed smooth muscle cells.

Actin Cytoskeleton↗
PubMed1997

Interhead distances in myosin attached to F-actin estimated by fluorescence energy transfer spectroscopy.

Fluorescence resonance energy transfer (FRET) spectroscopy has been used to determine distances between probes attached to the most reactive sulfhydryl (SH1) group on individual myosin "heads." We measured intramolecular and intermolecular interhead distances as well as the distance between one head of heavy meromyosin (HMM) mixed with subfragment-1 (S1) heads attached to F-actin under rigor conditions. The SH1 cysteine was specifically labeled with either a donor (5-((((2-iodoacetyl)amino)ethyl)amino)naphthalene-1-sulfonic acid) or an acceptor probe (5-iodoacetamidofluorescein). In free solution, the distance between these probes was too large to allow significant FRET, but in the rigor complex with F-actin, intermolecular interhead distances between S1 molecules, HMM molecules, or S1 and HMM were determined to be 6.0-6.3 nm. The radial coordinate of the labels relative to F-actin was 5.0-6.4 nm. However, the intramolecular interhead distance in HMMs in which the two heads were labeled with D and A probes was estimated to be larger. The binding affinity of the second head of HMM(D/A) to F-actin may be reduced because of heterogeneous modification of the SH1 groups, such that the probability of single-head binding is increased.

Actins↗
PubMed1980

Determination of hexamethylmelamine and metabolites in plasma or serum by gas-liquid chromatography with a nitrogen-sensitive detector.

A gas chromatographic method for the quantitative determination of hexamethylmelamine (HMM) and five of its metabolites in plasma (or serum) is described. After adjustment of the pH of the plasma sample to about 9.5, the compounds are extracted with chloroform containing 5% of isopropanol. Amyl alcohol is added to the extract, which is then evaporated until a small volume remains. An aliquot of this solution is injected into a gas chromatograph equipped with a nitrogen--phosphorus flame ionisation detector. Separation of the methylmelamines is achieved with a 10% Carbowax 20M--2% KOH column. By programming the oven temperature unnecessarily long retention times are avoided. Using 1 ml of plasma, concentrations as low as 5 ng/ml of HMM and its metabolites can be quantitated. The method has been applied to the determination of HMM and metabolites in plasma of patients who received oral doses of HMM.

Altretamine↗
PubMed1984

Tryptic digestion of rabbit skeletal myofibrils: an enzymatic probe of myosin cross-bridges.

Tryptic digestion of rabbit skeletal myofibrils under physiological ionic strength and pH conditions was used as a probe of cross-bridge interaction with actin in the presence of nucleotides and pyrophosphate. Under rigor conditions, digestion of myofibrils at 24 degrees C results in the formation of 25K, 110K [heavy meromyosin (HMM)], and light meromyosin (LMM) fragments as the main reaction products. Very little if any 50K peptide is generated in such digestions. In the presence of magnesium pyrophosphate, magnesium 5'-adenylyl imidodiphosphate (MgAMPPNP), and MgATP, the main cleavage proceeds at two positions, 25K and 75K from the N-terminal portion of myosin, yielding the 25K, 50K, and 150K species. The relative amounts of the 50K, 110K, and 150K peptides and the rates of myosin heavy-chain digestion in the presence of pyrophosphate and AMPPNP indicate partial dissociation of myosin from actin. Direct centrifugation measurements of the binding of HMM and subfragment 1 (S-1) to actin in myofibrils confirm that cross-bridges partition between attached and detached states in the presence of these ligands. In the presence of MgADP, HMM and S-1 remain attached to actin at 24 degrees C. However, tryptic digestion of myofibrils containing MgADP is consistent with the existence of a mixed population of attached and detached cross-bridges, suggesting that only one head on each myosin molecule is attached to actin. As shown by tryptic digestion of myofibrils and the measurements of HMM and S-1 binding to actin, nucleotide- and pyrophosphate-induced dissociation of cross-bridges is more pronounced at 4 than at 24 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Conformation of spin-labeled tropomyosin in reconstituted muscle thin filaments in response to calcium ion and heavy meromyosin.

Tropomyosin (TM) exists in thermal equilibrium between a highly structured N state, a partially unfolded X state, and a completely unfolded D state, i.e., N in equilibrium X in equilibrium D. The strongly immobilized electron spin resonance (ESR) spectral component of spin-labeled TM corresponds to TM in the N state and the weakly immobilized component to TM in the X state below the main unfolding transition and to TM in the D state above this transition [Graceffa, P., & Lehrer, S. S. (1984) Biochemistry 23, 2606-2612]. The addition of actin, troponin (TN), and heavy meromyosin (HMM) to spin-labeled TM reduces the ratio of weakly to strongly immobilized labels, indicating a shift in the N in equilibrium X in equilibrium D equilibrium toward the N state. At 37 degrees C, for spin-labeled TM alone K (=X/N) greater than 1.0 with some TM in the D state, K = 0.8 for spin-labeled TM bound to actin, and K less than 0.05 for spin-labeled TM bound to actin + TN +/- Ca2+, actin + HMM + TN +/- Ca2+, and actin + HMM. Thus, actin + TN dramatically shifts the TM structure to the N conformation with little further effect upon addition of Ca2+ or HMM. The temperature at which spin-labeled TM begins to dissociate from a protein complex was determined from the temperature dependence of the ESR spectra.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1982

Magnesium adenosine 5'-diphosphate influences proteolytic susceptibility of myosin in myofibrils.

The proteolytic susceptibility of the subfragment 2/light meromyosin junction [heavy meromyosin (HMM) junction] of myosin was employed as a probe of the cross-bridge conformation. The proteolysis was carried out in the myofibrils where myosin assembled in arrays typical of the in vivo organization. When subfragment I formation was inhibited by saturating the Nbs2 [5,5'-dithiobis(2-nitrobenzoic acid)] light chains with Mg2+ ions, chymotrypsin attacked exclusively the HMM junction. The rate of this attack was assessed by measuring the rate of HMM formation by quantitative polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and by following absorbance changes associated with the solubilization of myofibrillar suspensions. Under rigor conditions, the myofibrils were relatively resistant to the chymotryptic attack. The presence of MgAMP-PNP or MgPPi did not affect the rate of proteolytic attack. On the other hand, binding of MgADP had a powerful stimulating influence on the HMM site digestibility. The dissociation constant for the effect of MgADP was 10 microM less than Kd less than 50 microM. MgADP did not exercise its unique effect through destabilization of myosin filaments or through dissociation of the actomyosin complex. These results are explained in terms of a change in the myosin cross-bridge conformation brought about by the binding of MgADP to the active site.

Actomyosin↗
PubMed1976

Mechanism of inhibition of relaxation by N-ethylmaleimide treatment of myosin.

It has remained unexplained why N-ethylmalaeimide (NEM) treatment of myosin can inhibit relaxation in actomyosin systems from rabbit skeletal muscle which appear to be regulated solely through tropomyosin and troponin. Since rigor complexes between (nucleotide-free) myosin and actin affect the tropinin-tropomyosin system, the possibility was explored that, as a result of NEM treatment, some of the myosin maintains rigor complexes with actin in the presence of ATP which might be responsible for inhibition of relaxation. Evidence is presented indicating that such a mechanism might account for the effects of NEM treatment. First, after exhaustive NEM treatment of heavy meromysin (HMM), acto-HMM complexes were no longer dissociated by ATP. Second, admixture of such NEM-treated, enzymatically inactive HMM or myosin to native regulated actomyosin or acto-HMM inhibited relaxation.

Actins↗