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PubMedDate not supplied

Phase II study of hexamethylmelamine alone and in combination with mitomycin C and vincristine in advanced breast carcinoma.

Fifty-three patients with metastatic breast carcinoma were randomized to treatment with hexamethylmelamine (HMM) as a single agent versus a three-drug reimen of HMM, vincristine, and mitomycin C (HOM). All patients had received prior treatment with 5-fluorouracil, Adriamycin, and cyclophosphamide with or without methotrexate. HMM alone was used in a dose of 300 mg/m2/day x 14 days every 21 days. In the HOM regimen, the HMM dose was 200 mg/m2/day x 21 days, the vincristine dose was 1.5 mg on Days 1, 8, and 15, and the mitomycin C dose was 12 mg/m2 once every 6 weeks. No objective responses were observed with HMM in 15 evaluable patients. The HOM regimen resulted in five partial responses among the 27 evaluable patients. Gastrointestinal toxicity was the limiting toxicity of HMM, and thrombocytopenia was the major toxicity of the HOM regimen.

Adult↗
PubMed1977

18O-exchange catalyzed by myosin, heavy meromyosin, heavy meromyosin subfragment 1 and their complexes with actin.

Myosin, HMM and HMM S1 catalyze 18O-exchange between P1 and H218O of the medium at an intermediate stage of ATP hydrolysis ("intermediate 18O-exchange") in the presence of Mg2+. Natural complexes of actomyosin and acto-HMM S1 do not catalyze intermediate 18O-exchange but facilitate "direct" or "medium" 18O-exchange (KH2P18O4 in equilibrium H2O) even without ATP. Reconstituted complexes of actomyosin, acto-HMM, acto-HMM S1, PABC-HMM S1, congo-myosin and TNP-myosin do not catalyze direct 18O-exchange in the presence of Mg2+ and absence of ATP. From the data obtained a hypothetical sequence of phosphorylation and 18O-exchange reactions in myofibril action has been suggested.

Actins↗
PubMed1989

Characterization of thermotropic state changes in myosin subfragment-1 and heavy meromyosin by UV difference spectroscopy.

Thermotropic structural transitions in rabbit skeletal muscle heavy meromyosin and subfragment-1 (S-1) have been quantitatively investigated by using nucleotide-induced UV difference spectroscopy. The magnitude of the adenylyl 5'-imidophosphate (AMP-PNP)-induced difference spectrum is temperature-dependent for both S-1 and heavy meromyosin (HMM). The transition observed here appears to be the same transition observed by 31P NMR of bound AMP-PNP (Shriver, J., and Sykes, B. D. (1981) Biochemistry 20, 2004-2012). The ADP-induced spectrum is temperature-independent, which differs from the 31P NMR data, indicating that the chromophore contributing to the difference spectrum resides in a domain distinct from the active site, at least when ADP is bound. Although the magnitudes of the AMP-PNP-induced spectra are equal in magnitude for S-1 and HMM on a globular head basis, the temperature dependence of the AMP-PNP induced difference spectrum for S-1 differs significantly from that of HMM. The van't Hoff enthalpy for the apparent two-state transition in S-1 is half that observed with HMM: 19 (+/- 7.5) kcal/mol for S-1 and 35 (+/- 5) kcal/mol for HMM. This indicates an additional cooperative interaction in HMM which is not present in S-1. Modification of SH1 results in the loss of the temperature dependence of the AMP-PNP-induced difference spectrum, and the resulting difference spectra appear identical to those induced by ADP.

Animals↗
PubMed1985

Calcium-insensitive binding of heavy meromyosin to regulated actin at physiological ionic strength.

Several conflicting reports have been made regarding the affinity of myosin heads (subfragment 1 and heavy meromyosin (HMM) for regulated actin (actin complexed with tropomyosin and troponin) at low ionic strength (mu = 18-50 mM) and whether or not this interaction is Ca2+ sensitive (Chalovich, J. M., and Eisenberg, E. (1982) J. Biol. Chem. 257, 2432-2437; Chalovich, J. M., and Eisenberg, E. (1984) Biophys. J. 45, 221a; Wagner, P. D., and Stone, D. B. (1983) Biochemistry 22, 1334-1342; and Wagner, P. D. (1984) Biochemistry 23, 5950-5956). Since the low ionic strengths used in the above studies do not represent the physiological ionic strength under which intact muscle exhibits Ca2+-dependent tension development, we investigated the possibility of whether a Ca2+-dependent regulated actin-HMM interaction could be observed at physiological ionic strength (mu = 134 mM, pH 7.4) and in the presence of ATP (at 23-24 degrees C). Direct binding of HMM to varied concentrations of regulated actin (87.7-221 microM free actin) was measured by sedimentation in an air-driven ultracentrifuge. Under the above conditions, we found that the regulated actin activation of HMM-Mg2+-ATPase was about 94% inhibited in the absence of Ca2+ although the association constant (Ka) is only moderately affected in the presence of Ca2+. These results are similar to those obtained by Chalovich and Eisenberg (1982 and 1984) with subfragment 1 and HMM, respectively, at low ionic strength and support their suggestion that in solution tropomyosin-troponin may not act totally by physically blocking the formation of cross-bridges with actin, but instead may act to inhibit a kinetic step in the overall ATPase rate. Whether this holds true in more intact systems (e.g. myosin, thick filaments) remains to be determined. Our results also show a good correlation between levels of ATPase activation and HMM binding by unregulated actin and in regulated actin in the presence of Ca2+.

Actins↗
PubMed1969

Formation of arrowhead complexes with heavy meromyosin in a variety of cell types.

Heavy meromyosin (HMM) forms characteristic arrowhead complexes with actin filaments in situ. These complexes are readily visualized in sectioned muscle. Following HMM treatment similar complexes appear in sectioned fibroblasts, chondrogenic cells, nerve cells, and several types of epithelial cells. Thin filaments freshly isolated from chondrogenic cells also bind HMM and form arrowhead structures in negatively stained preparations. HMM-filament complexes are prominent in the cortex of a variety of normal metaphase and Colcemid-arrested metaphase cells. There is no detectable binding of HMM with other cellular components such as microtubules, 100-A filaments, tonofilaments, membranes, nuclei, or collagen fibrils. The significance of HMM-filament binding is discussed in view of the finding that arrowhead complexes form in types of cells not usually thought to contain actin filaments.

Animals↗
PubMed1983

The apparently negatively cooperative phosphorylation of smooth muscle myosin at low ionic strength is related to its filamentous state.

The correlation curve between phosphorylation and MgATPase activity suggests that the 20,000-dalton light chain of both heads of a smooth muscle myosin or heavy meromyosin (HMM) molecule must be phosphorylated before the MgATPase activity of either head can be activated by actin. The two heads of HMM appear to be phosphorylated randomly at equal rates, while those of myosin are phosphorylated in a negatively cooperative manner (Persechini, A., and Hartshorne, D.J. (1981) Science, 213, 1383-1385; Ikebe, M., Ogihara, S., and Tonomura, Y. (1982) J. Biochem. 91, 1809-1812). We have investigated the cause of this difference between HMM and myosin. We find that if myosin is first phosphorylated at high ionic strength (0.6 M KCl), where it is monomeric, and then assayed for MgATPase activity (in 0.05 M KCl), the data support a model where the two heads are phosphorylated randomly with equal rates (i.e. similarly to HMM). The correlation curves between MgATPase activity and dephosphorylation of fully phosphorylated myosin, both in a filamentous and monomeric state, are also best explained by a model where dephosphorylation of one head is sufficient to deactivate the entire molecule. With monomeric myosin, the dephosphorylation appears to occur randomly with equal rates, whereas with filamentous myosin the dephosphorylation appears to be negatively cooperative. The correlation between dephosphorylation of HMM and its MgATPase activity is more complex and is consistent with a positively cooperative dephosphorylation. Direct analyses of the time courses of phosphorylation of HMM and monomeric myosin show that a single exponential is sufficient to fit the data through greater than 90% of the reaction. However, when phosphorylation is carried out at low ionic strength (0.02 M KCl), where myosin is present as filaments, the time course consists of two exponential functions where the rate constant for the phosphorylation of one myosin head is 6-10 times greater than that for the other head which is located on the same molecule. This suggests that when myosin is polymerized into filaments the two previously indistinguishable heads either become nonequivalent or are subject to head-head interactions leading to a negatively cooperative phosphorylation reaction.

Actins↗
PubMed1983

Role of N-methylolpentamethylmelamine in the metabolic activation of hexamethylmelamine.

Hexamethylmelamine (HMM) is metabolized by rat hepatic microsomal preparations to reactive species which covalently bind to microsomal protein and to calf thymus DNA added to microsomal incubation mixtures. Covalent binding to macromolecules is dependent on the presence of molecular oxygen and reduced nicotinamide adenine dinucleotide phosphate and is catalyzed by cytochrome P-450 monooxygenases. Reduced nicotinamide adenine dinucleotide-dependent covalent binding of [methyl-14C]HMM to microsomal protein is greater than that of [ring-14C]HMM. Reduced nicotinamide adenine dinucleotide phosphate-dependent covalent binding of [ring-14C]HMM and [methyl-14C]HMM to calf thymus DNA added to microsomal incubation mixtures are approximately equal. The [ring-14C]-labeled carbinolamine intermediate in HMM demethylation, N-methylolpentamethylmelamine, covalently binds to microsomal protein and, to a much greater extent, to calf thymus DNA.

Altretamine↗
PubMed1981

Hexamethylmelamine chemotherapy for disseminated endometrial cancer.

To evaluate the role of hexamethylmelamine (HMM) in the treatment of endometrial cancer, 20 women with metastatic or recurrent endometrial carcinoma received HMM orally at a dose of 8 mg/kg/day. Six patients (30%) showed a partial response, with a median duration of response of 3.5 months and a range of 1 to 7 months. Two patients responded to HMM as a second-line agent following previous treatment with nonhormonal chemotherapy. There were no complete responses. The major toxicities noted with HMM therapy were nausea, vomiting, and neurotoxicity. In 6 patients (30%), therapy with HMM was discontinued because of toxicity. Although HMM is active against endometrial cancer when given at a dose of 8 mg/kg/day, it appears to have limited usefulness because toxicity precludes its prolonged administration.

Aged↗
PubMed1982

Parenteral formulation of hexamethylmelamine potentially suitable for use in man.

We have developed a preparation of hexamethylmelamine (HMM), dissolved in a fat emulsion Intralipid 20%, that is potentially satisfactory for parenteral administration to man. Solid HMM can be dissolved in Intralipid 20% up to 5 mg/ml, with extensive agitation. Solubilization of HMM is facilitated first by dissolving the drug in ethanol or in dimethylacetamide and then by adding the solution to Intralipid 20%. The disposition of HMM in rabbits after iv administration of HMM dissolved in Intralipid 20% was similar to the disposition of the drug following iv administration of HMM dissolved in 0.1 N HCl.

Altretamine↗
PubMed1993

Hidden Markov models and iterative aligners: study of their equivalence and possibilities.

There are many shared attributes between existing iterative aligners and Hidden Markov Model (HMM). A learning algorithm of HMM called Viterbi is the same as the iteration of DP-matching of iterative aligners. HMM aligners can use the result of an iterative aligner initially, incorporate the similarity score of amino acids, and apply the detailed gap cost systems to improve the matching accuracy. On the other hand, the iterative aligner can inherit the modeling capability of HMM, and provide the better representation of the proteins than motifs. In this paper, we present an overview of several iterative aligners which include the parallel iterative aligner of ICOT and the HMM aligner of Haussler's group. We compare the merits and shortcomings of these aligners. This comparison enables us to formulate a better, more advanced aligner through proper integration of the iterative technique and HMM technique.

Algorithms↗
PubMed1995

Single-molecule mechanics of heavy meromyosin and S1 interacting with rabbit or Drosophila actins using optical tweezers.

Single-molecule mechanical interactions between rabbit heavy meromyosin (HMM) or subfragment 1 (S1) and rabbit actin were measured with an optical tweezers piconewton, nanometer transducer. Similar intermittent interactions were observed with HMM and S1. The mean magnitude of the single interaction isotonic displacements was 20 nm for HMM and 15 nm with S1. The mean value of the force of single-molecule interactions was 1.8 pN for HMM and 1.7 pN with S1. The stiffness of myosin S1 was determined by applying a sinusoidal length change to the thin filament and measuring the corresponding force; the mean stiffness was 0.13 pN nm-1. By moving an actin filament over a long distance past an isolated S1 head, we found that cross-bridge attachment occurred preferentially at a periodicity of about 40 nm, similar to that of the actin helical repeat. Rate constants for the probability of detachment of HMM from actin were determined from histograms of the lifetime of the attached state. This gave a value of 8 s-1 or 0.8 x 10(6) M-1 s-1 for binding of ATP to the rigor complex. We conclude (1) that our HMM-actin interactions involve just one head, (2) that compliance of the cross-bridge is not in myosin subfragment 2, although we cannot say to what extent contributions arise from myosin S1 or actin, and (3) that the elemental movement can be caused by a change of shape of the S1 head, but that this would have to be much greater than the movements suggested from structural studies of S1 (Rayment et al., 1993).

Actins↗
PubMed1976

Immobilized ATP and actin columns as a tool for the characterization and separation of different myosins and active myosin fragments.

A comparative affinity chromatography study using agarose-ATP columns revealed differences between heavy meromyosin subfragment 1 (HMM S-1) preparations obtained from rabbit white skeletal, rabbit red skeletal, bovine cardiac, and chicken gizzard muscle myosins. The characteristic patterns were markedly affected by Ca2+ and Mg2+ ions in a manner typical for each myosin species. Similar differences were also observed on comparing the intact myosins of red and white muscles. It thus became possible to separate, at least partially, mixtures of myosin (or HMM S-1) of different origins. Muscle "acetone-dried powder" was used as chromatographic medium for active myosin fragments in affinity chromatography columns. At low ionic strength the columns bound appreciable amounts of heavy meromyosin (HMM) and of HMM S-1. Binding was reversible and the myosin fragments could be eluted by ATP or magnesium pyrophosphate. The absorption peak of bovine cardiac HMM S-1 was found to be less symmetrical than that of the rabbit white skeletal analog. Chemical modification by trinitrophenylation of white skeletal HMM S-1 was found to affect the affinity of binding and the shape of the absorption peak, thus enabling a partial separation of trinitrophenylated fragment from the unmodified protein using an actin column. The resolving power of ATP columns for the separation of red and white skeletal myosins was increased after trintrophenylation of the proteins.

Actins↗
PubMed1996

Extraction of hidden Markov model representations of signal patterns in DNA sequences.

We have developed a method to extract the signal patterns in DNA sequences. In this method, the Genetic Algorithm (GA) and Baum-Welch algorithm are used to obtain the best Hidden Markov Model (HMM) representations of the signal patterns in DNA sequences. The GA is used to search the best network shapes and the initial parameters of the HMMs. Baum-Welch algorithm is used to optimize the HMM parameters for the given network shapes. Akaike Information Criterion (AIC), which gives a criterion for the balance of adaptation and complexity of a model, is applied in the HMM evaluation. We have applied the method to the extraction of the signal patterns in human promoters and 5' ends of yeast introns. As a result, we obtained HMM representations of characteristic features in these sequences. To validate the efficiency of the method, we have performed promoter recognition using obtained HMMs. Two entries including nine promoters are selected from GenBank 76.0, and it is observed that the HMM can predicts eight promoters correctly. These results imply that the method is efficient to design preferable HMM networks, and provides reliable models for the recognition of the signal patterns.

Algorithms↗
PubMed1998

Smooth muscle myosin. Amino acid residues responsible for the hydrolysis of ATP.

From their crystallographic comparisons, Fisher et al. (Biochemistry 34, 8960-8972, 1995) have proposed that in an important transition of myosin heads (M), M.ATP-->M.ADP.Pi, an interdomain rotation occurs in Gly468 (of chicken smooth muscle myosin) and that the rotated state is stabilized by newly-formed interdomain contacts including the salt link between Glu470 and Arg247 (of chicken smooth muscle myosin). Here, we have studied the effects of Gly468, Glu470, and Arg247 mutations on the hydrolysis of ATP. The G468A HMM did not show a significant ATPase activity, a stoichiometric initial phosphate burst, and tryptophan fluorescence enhancement attributed to bound ADP.Pi. The E470A HMM also did not show a significant ATPase activity and the phosphate burst, but the mutant gave tryptophan response attributed to bound ATP. The E470R/R247E HMM exhibited an ATPase activity and the phosphate burst which were comparable to those of the wild-type HMM, whereas neither the E470R HMM nor the R247E HMM showed such a significant ATPase activity and burst. We thus propose that both an unhindered rotation and a salt link that stabilizes the rotated state are necessary for ATP hydrolysis.

Adenosine Triphosphate↗
PubMed2003

Quinidine impairs proliferation of neurofibromatosis type 2-deficient human malignant mesothelioma cells.

BACKGROUND: Human malignant mesotheliomas (HMMs) are aggressive tumors that arise from the mesothelium. They respond poorly to conventional tumor treatment and outcome is often fatal. Inactivating mutations of the neurofibromatosis type 2 (NF2) tumor suppressor gene merlin have been described in nearly 60% of primary malignant mesothelioma and in approximately 20% of the mesothelioma cell lines. Studies regarding human NF2 schwannoma cells revealed a higher proliferation and a larger noninactivating K(+) outward current compared with controls. The enhanced proliferation of merlin-deficient NF2 schwannoma cells could be reduced in the presence of quinidine, a K(+) channel blocker, whereas the proliferation of normal Schwann cells is not affected. The current study was undertaken to evaluate the effect of quinidine on the proliferation of HMM cell lines in relation to their NF2 status. METHODS: Proliferation analyses using bromodeoxyuridine incorporation was performed by immunocytochemical staining and fluorescence assisted cell sorting. The patch-clamp technique was applied for electrophysiologic characterization of the HMM cell lines. The cytochrome P450 2D6 locus, known to be mutated at high frequencies in NF2 patients and to be specifically inhibited by quinidine, was screened for mutations by cycle sequencing. RESULTS: Quinidine selectively reduces the proliferation of merlin-deficient HMM cell lines by causing a G(0)/G(1) arrest, whereas the proliferation rates of merlin-expressing HMM cell lines remain unchanged. The effect of quinidine on the proliferation of HMM cell lines appears to be correlated with the NF2 gene status but not with the K(+) outward current. No relation to cytochrome P450 2D6 mutations was detected. CONCLUSIONS: Quinidine or quinidine analogs are of potential therapeutic interest for the subset of merlin-deficient mesothelioma tumors.

Blotting, Western↗
PubMed2004

A hidden Markov modeling approach for admixture mapping based on case-control data.

Admixture mapping is potentially a powerful method for mapping genes for complex human diseases, when the disease frequency due to a particular disease-susceptible gene is different between founding populations of different ethnicity. The method tests for association of the allele ancestry with the disease. Since the markers used to define ancestral populations are not fully informative for the ancestry status, direct test of such association is not possible. In this report, we develop a unified hidden Markov model (HMM) framework for estimating the unobserved ancestry haplotypes across a chromosomal region based on marker haplotype or genotype data. The HMM efficiently utilizes all the marker data to infer the latent ancestry states at the putative disease locus. In this HMM modelling framework, we develop a likelihood test for association of allele ancestry and the disease risk based on case-control data. Existence of such association may imply linkage between the candidate locus and the disease locus. We evaluate by simulations how several factors affect the power of admixture mapping, including sample size, ethnicity relative risk, marker density, and the different admixture dynamics. Our simulation results indicate correct type 1 error rates of the proposed likelihood ratio tests and great impact of marker density on the power. The simulation results also indicate that the methods work well for the admixed populations derived from both hybrid-isolation and continuous gene-flowing models. Finally, we observed that the genotype-based HMM performs very similarly in power as the haplotype-based HMM when the haplotypes are known and the set of markers is highly informative.

Alleles↗
PubMed1996

The mechanism for mechanochemical energy transduction in actin-myosin interaction revealed by in vitro motility assay with ATP analogues.

We investigated in vitro motility of F-actin on heavy meromyosin (HMM) and nucleotide triphosphatase activity of acto-HMM by using ATP analogues of various nucleotide triphosphates (NTPs) and enzymatically cleaved actins. The sliding velocity did not correlate with the actin activated HMM-NTPase activity, but correlated strongly with the reciprocal of NTPase activity of HMM itself, i.e., the cycle time of HMM NTPase. This indicated that with ATP the complex of myosin with the product, M.ADP.Pi, at the long lived intermediate state of the rate limiting step would play a key role for efficient mechanochemical energy transduction during actin-myosin interaction.

Actins↗
PubMed2001

Calcium-dependent structural changes in scallop heavy meromyosin.

The mechanism of calcium regulation of scallop myosin is not understood, although it is known that both myosin heads are required. We have explored possible interactions between the heads of heavy meromyosin (HMM) in the presence and absence of calcium and nucleotides by sedimentation and electron microscope studies. The ATPase activity of the HMM preparation was activated over tenfold by calcium, indicating that the preparation contained mostly regulated molecules. In the presence of ADP or ATP analogs, calcium increased the asymmetry of the HMM molecule as judged by its slower sedimentation velocity compared with that in EGTA. In the absence of nucleotide the asymmetry was high even in EGTA. The shift in sedimentation occurred with a sharp midpoint at a calcium level of about 0.5 microM. Sedimentation of subfragment 1 was not dependent on calcium or on nucleotides. Modeling accounted for the observed sedimentation behavior by assuming that both HMM heads bent toward the tail in the absence of calcium, while in its presence the heads had random positions. The sedimentation pattern showed a single peak at all calcium concentrations, indicating equilibration between the two forms with a t(1/2) less than 70 seconds. Electron micrographs of crosslinked, rotary shadowed specimens indicated that 81 % of HMM molecules in the presence of nucleotide had both heads pointing back towards the tail in the absence of calcium, as compared with 41 % in its presence. This is consistent with the sedimentation data. We conclude that in the "off" state, scallop myosin heads interact with each other, forming a rigid structure with low ATPase activity. When molecules are switched "on" by binding of calcium, communication between the heads is lost, allowing them to flex randomly about the junction with the tail; this could facilitate their interaction with actin in contracting muscle.

Animals↗