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R Kassab

Publications and source records attributed to R Kassab.

At least 55 records · Page 3Linked to original sources
PubMed1988

The myosin SH2-50-kilodalton fragment cross-link: location and consequences.

Some of us recently described a new interthiol cross-link which occurs in the skeletal myosin subfragment 1-MgADP complex between the reactive sulfhydryl group "SH2" (Cys-697) and a thiol (named SH chi) of the 50-kilodalton (kDa) central domain of the heavy chain; this link leads to the entrapment of the nucleotide at the active site [Chaussepied, P., Mornet, D., & Kassab, R. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 2037-2041]. In the present study, we identify SH chi as Cys-540 of the 50-kDa fragment. The portion of the heavy chain including this residue and also extending to Cys-522 that is cross-linkable to the "SH1" thiol [Ue, K. (1987) Biochemistry 26, 1889-1894] is near the SH2-SH1 region. Furthermore, various spectral and enzymatic properties of the (Cys697-Cys540)-N,N'-p-phenylenedimaleimide (pPDM)-cross-linked myosin chymotryptic subfragment 1 (S-1) were established and compared to those for the well-known (SH1-SH2)-pPDM-cross-linked S-1. The circular dichroism spectra of the new derivative were similar to those of native S-1 complexed to MgADP. At 15 mM ionic strength, (Cys697-Cys540)-S-1 binds very strongly to unregulated actin (Ka = 7 X 10(6) M-1), and the actin binding is very weakly affected by ionic strength. Joining actin with the (Cys697-Cys540)-S-1 heavy chain, using 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide, produces different species than does joining unmodified S-1 with actin.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1987

Comparative structure of the protease-sensitive regions of the subfragment-1 heavy chain from smooth and skeletal myosins.

The heavy chain fragments generated by restricted proteolysis of the smooth chicken gizzard myosin subfragment-1 (S-1) with trypsin, Staphylococcus aureus V8 protease, and chymotrypsin were isolated and submitted to partial amino acid sequencing. The comparison between the smooth and striated muscle myosin sequences permitted the unambiguous structural characterization of the two protease-vulnerable segments joining the three putative domain-like regions of the smooth head heavy chain. The smooth carboxyl-terminal connector is a serine-rich region located around positions 632-640 of the rabbit skeletal sequence and would represent the "A" site that is conformationally sensitive to the myosin 10 S-6 transition and to its interaction with actin (Ikebe, M., and Hartshorne, D. J. (1986) Biochemistry 25, 6177-6185). A third site which undergoes a nucleotide-dependent chymotryptic cleavage which inactivates the Mg2+-ATPase (Okamoto, Y., and Sekine, T. (1981) J. Biochem. (Tokyo) 90, 833-842, 843-849) was identified at Trp-31/Ser-32. It is vicinal to Lys-34 that is monomethylated in the skeletal heavy chain but not at all in the smooth sequence. However, the two trimethyl lysine residues present in the skeletal sequence are conserved in the same regions of the smooth S-1 and may play a general functional role in myosin. The smooth central 50-kDa segment could be selectively destroyed by a mild tryptic digestion in the absence of any unfolding agent, with a concomitant inhibition of the ATPase activities. This feature is in line with the proposed domain structure of the S-1 heavy chain and also suggests a relationship between the specific biochemical properties of the smooth S-1 and the particular conformation of its 50-kDa region.

Amino Acid Sequence↗
PubMed1986

Specific interactions of the alkali light chain 1 in skeletal myosin heads probed by chemical cross-linking.

We have investigated the enzymatic properties of the 120K cross-linked heavy-chain-light-chain derivative formed upon reaction of chymotryptic myosin subfragment 1 (S-1) isoenzymes with the bis(imido esters) dimethyl 3,3'-dithiobis(propionimidate) and dimethyl suberimidate. The formation of the 120K product was accompanied for S-1(A1) but not for S-1(A2) by a loss of the actin-activated ATPase without alteration of the Ca2+-ATPase whereas the Mg2+-ATPase was increased 2-fold. Up to 70%, the inhibition of the acto-S-1(A1) ATPase activity was closely correlated with the extent of cross-linking of the A1 light chain; this activity could be largely restored upon cleavage of the cross-link using the reversible cross-linker dimethyl 3,3'-dithiobis(propionimidate). The covalent link affected the acto-S-1(A1) Mg2+-ATPase activity by reducing 3-fold the Vmax and increasing 2-fold the Kapp. On reacting for the first time the hydrophobic, carboxyl group directed cross-linker N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) with the acto-S-1(A1 + A2) complex, we found that the N-terminal tail of the A1 light chain was cross-linked to actin to an extent much larger than observed earlier with the water-soluble 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide; like the latter agent, EEDQ elicited the covalent union of the A1 subunit to the COOH-terminal part of actin. This cross-linker appears to be a valuable chemical probe of the F-actin-A1 light-chain interaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1986

Identification of polyphosphate recognition sites communicating with actin sites on the skeletal myosin subfragment 1 heavy chain.

Using the thrombin-cut [68-30 kilodalton (kDa)] myosin subfragment 1 (S-1) whose heavy chain has been selectively split within the central 50-kDa region, at Lys-560, with concomitant specific alterations of the ATPase and actin binding properties [Chaussepied, P., Mornet, D., Audemard, E., Derancourt, J., & Kassab, R. (1986) Biochemistry 25, 1134-1140; Chaussepied, P., Mornet, D., Barman, T., Travers, F., & Kassab, R. (1986) Biochemistry 25, 1141-1149], we have isolated and renatured the COOH-terminal 30-kDa fragment associated with the alkali light chains by the procedure recently described [Chaussepied, P., Mornet, D., Audemard, E., Kassab, R., Goodearl, J., Levine, B., & Trayer, I. P. (1986) Biochemistry 25, 4540-4547]. The 30-kDa peptide preparation was found to exhibit a crucial feature of the native S-1; namely, it interacts with F-actin in an adenosine 5'-triphosphate (ATP)-dependent manner. Studies by ultracentrifugation, turbidity measurements, and chemical cross-linking experiments showed that the acto-30-kDa peptide complex was dissociated almost completely by the gamma-phosphoryl group containing ligands ATP, 5'-adenylyl imidodiphosphate, and pyrophosphate, to a lesser extent by ADP, and not at all by AMP and inorganic phosphate. The maximal dissociating effect is operating with the thrombic 30-kDa entity, whereas the 22-kDa fragment produced by staphylococcal protease is only slightly dissociated. In contrast, the tryptic 20-kDa fragment binds irreversibly to actin.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1986

Properties of the alkali light-chain-20-kilodalton fragment complex from skeletal myosin heads.

We have developed a rapid and reproducible procedure widely applicable to the preparation of pure aqueous solutions of the complex between an alkali light chain and the COOH-terminal heavy-chain fragments of skeletal myosin chymotryptic subfragment 1 (S-1) split by various proteases. It was founded on the remarkable ethanol solubility of these complexes. A systematic study of the ethanol fractionation of the tryptic (27K-50K-20K)-S-1 (A2) showed the NH2-terminal 27K fragment to behave like a specific protein entity being quantitatively precipitated at a relatively low ethanol concentration. Only the 20K peptide-A2 complex remained in solution when the S-1 derivative was treated with exactly 4 volumes of ethanol in the presence of 6 M guanidinium chloride. At a lower ethanol concentration, a soluble mixture of 50K and 20K peptides together with the light chain was obtained. The isolated 20K fragment-A2 system containing a 1:1 molar ratio of each component was investigated by biochemical and 1H nuclear magnetic resonance (NMR) techniques to highlight its structure and the interaction of the 20K heavy-chain segment with F-actin and with the light chain. During the treatment of the complex with alpha-chymotrypsin, only the 20K peptide was fragmented in contrast to its stability within the whole S-1. The binding of F-actin to the complex led, however, to a strong inhibition of its chymotryptic degradation. 1-Ethyl-3-[3-(dimethylamino)propyl]carbodiimide cross-linking of F-actin to the complex produced covalent actin-20K peptide only, the amount of which was lower relative to that observed with the entire split S-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1986

Characterization of the Ca2+-induced conformational changes in gelsolin and identification of interaction regions between actin and gelsolin.

Serum gelsolin, a Ca2+-dependent protein regulating the length of actin filaments, undergoes conformational changes upon binding Ca2+. These were detected and analyzed by several approaches including ultraviolet difference spectroscopy, circular dichroism studies, analytical ultracentrifugation, thiol group titration, and limited proteolytic digestions. The effect of Ca2+ binding on the UV absorption difference spectrum and the near-UV circular dichroism spectrum was consistent with changes in the environments of tyrosine and phenylalanine residues. In the presence of Ca2+, the S0(20),w value decreased from 5.3 to 4.7. This latter result implies a transformation to a more asymmetric molecular shape. Gelsolin contained only two accessible thiol groups per mole of protein, one of which was titratable in the native protein; it was more accessible to 5,5'-dithiobis(2-nitrobenzoic acid) in the absence than in the presence of Ca2+. The limited digestion of gelsolin from serum and bovine aorta smooth muscle by two different proteases, chymotrypsin and trypsin, proceeded much faster in the presence of Ca2+ than in its absence with the production of three main fragments of about 40K, 32K, and 21K. This fragment mixture was found still able to shorten F-actin in a Ca2+-dependent manner; this severing activity was expressed by the isolated 40K peptide. Gelsolin was cross-linked to F- and G-actin by the zero-length cross-linker 1-ethyl-3-[3-(dimethylamino)propyl]-carbodiimide (EDC), generating a covalent 130K binary complex (actin1-gelsolin1) followed by a covalent 180K ternary complex (actin2-gelsolin1).(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1986

Abolition of ATPase activities of skeletal myosin subfragment 1 by a new selective proteolytic cleavage within the 50-kilodalton heavy chain segment.

We have isolated and chemically characterized several 5-thio-2-nitrobenzoate-subfragment 1 derivatives (TNB-S-1) generated by the reaction of 5,5'-dithiobis(2-nitrobenzoic acid) (DNTB, up to 10-fold molar excess) with native S-1, N-acetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine-S-1 (AEDANS-S-1), and N,N'-p-phenylenedimaleimide-S-1 (pPDM-S-1) at 4 degrees C, pH 8.0. The reaction of the reagent with AEDANS-S-1, which has a blocked -SH1 group, induced the formation of an intramolecular cystine disulfide between two vicinal -SH groups in S-1; in contrast, the treatment of pPDM-S-1 with DTNB resulted in the formation of TNB mixed disulfides only. The incorporation of the TNB groups (up to 3 mol/mol of S-1) into the native or premodified S-1 led to a local conformational change in the 50K heavy chain region that was fully reversed upon disulfide reduction. Exploiting this peculiarity of the DTNB-modified S-1's, we have realized a highly selective proteolysis of the S-1 heavy chain by thrombin and chymotrypsin, which do not act at all on the normal S-1. The 95K heavy chain was cut by thrombin into two fragments with apparent masses of 68K and 30K, whereas the "connector segments" and the light chains were unaffected. The two new fragments were issued from a primary peptide-bound cleavage between Lys-560 and Ser-561 within the amino acid sequence of the 50K region (M. Elzinga, personal communication).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1986

Alteration of the ATP hydrolysis and actin binding properties of thrombin-cut myosin subfragment 1.

We have characterized various structural and enzymatic properties of the (68K-30K)-S-1 derivative obtained by thrombic cleavage [Chaussepied, P., Mornet, D., Audemard, E., Derancourt, J., & Kassab, R. (1986) Biochemistry (preceding paper in this issue)]. The far-ultraviolet CD spectra and thiol reactivity measurements indicated an unchanged overall polypeptide conformation of the enzyme whereas the CD spectra in the near-ultraviolet region suggested a local change in the environments of phenylalanine side chains; the latter finding was rationalized by considering the existence of about five of these amino acids in the vicinity of the cleavage sites. When the binding of Mg2+-ATP and Mg2+-ADP to the derivative was assessed by CD spectroscopy, distinct spectra were obtained with the two nucleotides as with native subfragment 1 (S-1), but some spectral features were unique to the nicked S-1. Stern-Volmer fluorescence quenching studies using acrylamide and the analogues 1,N6-ethenoadenosine 5'-triphosphate and 1,N6-ethenoadenosine 5'-diphosphate indicated that the complexes formed with the modified S-1 have a solute quencher accessibility close to that observed for the complexes with the normal S-1. However, in contrast to the parent enzyme, the thrombin-cut S-1 was unable to bind irreversibly Mg2+-ATP, nor did it form a stable Mg2+-ADP-sodium vanadate complex or achieve the entrapping of Mg2+-ADP after cross-linking of SH1 and SH2 with N,N'-p-phenylenedimaleimide. Additionally, the amplitude of the Pi burst was very low, indicating that the inactivation of the proteolyzed S-1 was linked to the suppression of the hydrolysis step in the ATPase cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1986

Nucleotide trapping at the ATPase site of myosin subfragment 1 by a new interthiol crosslinking.

When myosin subfragment 1 derivatives in which the reactive sulfhydryl SH1 has been blocked react with N,N'-p-phenylenedimaleimide or 5,5'-dithiobis(2-nitrobenzoic acid), the reactive sulfhydryl group SH2 of the 20-kDa domain is crosslinked with a thiol of the 50-kDa domain of the heavy chain. The crosslink induces the stable trapping of a significant amount of Mg2+-nucleotide in the ATPase site.

Adenine Nucleotides↗
PubMed1986

[Midpoint follow-up results of aortic valve replacement with the Ionescu-Shiley pericardial bioprosthesis. Apropos of 109 patients].

Between March 1980 and May 1985, 109 adults with an average age of 59 years underwent aortic valve replacement with a pericardial Ionescu-Shiley xenograft. Twenty six of the prostheses were of small size (N 19 and 21). In 20 patients, the operation was associated with another procedure (15 aorto coronary bypass grafts and 5 conservative mitral valve procedures). Before surgery, 73.4% of patients were in functional Stages III or IV, and 9.2% had permanent or paroxysmal atrial fibrillation. The average follow-up period was 24 months (4 to 59). The operative mortality was 5.5%. The 4 year actuarial survival rate was 86% with 82% good functional results. At the same date, 96.4% of patients had not developed endocarditis, 96% had not been reoperated and 93.8% had no prosthetic valve dysfunction. No cases of primary degeneration were observed but a diastolic murmur without any haemodynamic consequences was detected in 20% of patients at 4 years. Seventy four per cent of subjects were not anticoagulated at 1 year and 85% were without anticoagulants after one year. Only one haemorrhagic complication was noted (0.46% patient/years). There were no cases of occlusive thrombosis; the incidence of thromboembolism was 3.7% patient/years in aortic without mitral valve disease, irrespective of the cardiac rhythm and 2.7% patient/years in patients in sinus rhythm. In this subgroup, 88% had not had any thrombo-embolic complication despite the absence of anticoagulants at 4 years. An Indium III labelled platelet scan was positive in 2 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Transient kinetics of adenosine 5'-triphosphate hydrolysis by covalently cross-linked actomyosin complex in water and 40% ethylene glycol by the rapid flow quench method.

The initial steps of the ATPase of covalently cross-linked actomyosin subfragment 1 (acto-SF-1) were studied by the rapid flow quench method, and the results obtained were compared with those with reversible (i.e., non-cross-linked) acto-SF-1 and SF-1 under identical conditions. Cross-linked acto-SF-1 plus [gamma-32P]ATP reaction mixture milliseconds old was quenched either in a large excess of unlabeled ATP (ATP chase) or in acid (Pi burst). The conditions were pH 8 and 15 degrees C at 5 mM or 0.15 M KCl and with or without 40% ethylene glycol. In 40% ethylene glycol (5 mM KCl), as with SF-1 and reversible acto-SF-1, the ATP chase was used to titrate active sites and to study the kinetics of ATP binding. Unlike those with SF-1 or reversible acto-SF-1, saturation kinetics were not obtained. The second-order rate constant for ATP binding was 3.1 X 10(6) M-1 s-1 for cross-linked acto-SF-1, 1.8 X 10(6) M-1 s-1 for reversible acto-SF-1, and 2 X 10(6) M-1 s-1 for SF-1. In Pi burst experiments, a transient phase could not be discerned. Because of a high kcat, cross-linked acto-SF-1 was difficult to study in aqueous solution, but at 5 mM KCl, the ATP chase and Pi burst curves were similar to those obtained in 40% ethylene glycol. At 0.15 M KCl the ATP chase curve was difficult to interpret (small amplitude), and there was a small Pi burst.(ABSTRACT TRUNCATED AT 250 WORDS)

Actomyosin↗
PubMed1985

Molecular movements promoted by metal nucleotides in the heavy-chain regions of myosin heads from skeletal muscle.

Molecular movements generated in the heavy-chain regions (27-50-20(X 10(3)) Mr) of myosin S1 on interaction with nucleotides ATP, AMPPNP, ADP and PPi were investigated by limited proteolysis of several enzyme-metal nucleotide complexes in the absence and presence of reversibly bound and crosslinked F-actin. The rate and extent of the nucleotide-promoted conversion of the NH2-terminal 27 X 10(3) Mr and 50 X 10(3) Mr segments into products of 22 X 10(3) Mr and 45 X 10(3) Mr, respectively, were estimated to determine the amplitude of the molecular movements. The 22 X 10(3) Mr peptide was identified by amino acid sequence studies as being derived from cleavage of the peptide bond between Arg and Ile (at position 23 to 24). The 45 X 10(3) Mr peptide, previously shown to represent the NH2-terminal part of the 50 X 10(3) Mr region, would be connected to the adjacent C-terminal 20 X 10(3) Mr region by a pre-existing loop segment of about 5 X 10(3) Mr; the proteolytic sensitivity of the latter region is increased particularly by nucleotide binding. The tryptic reaction proved to be a sensitive indicator of the conformational state of the liganded heavy chain as the rate of peptide bond cleavage in the two regions is dependent on the nature of the bound ligand; it decreases in the order: ATP greater than AMPPNP greater than ADP greater than PPi. It depends also on the nature of the metal present, Mg2+ and Ca2+ being much more effective than K+. Binding of F-actin to the S1-MgAMPPNP complex affords significant protection against breakdown of 27 X 10(3) Mr and 50 X 10(3) Mr peptides, but with concomitant hydrolysis of the 50 X 10(3) Mr-20 X 10(3) Mr junction. Additionally, interaction of MgATP with HMM modulates the tryptic fission of the S1-S2 region. The overall data provide a molecular support for the two-state model of the myosin head and emphasize the involvement of the 50 X 10(3) Mr unit in the mechanism of coupling between the actin and nucleotide binding sites.

Actins↗
PubMed1985

Interaction of the heavy chain of gizzard myosin heads with skeletal F-actin.

To probe the molecular properties of the actin recognition site on the smooth muscle myosin heavy chain, the rigor complexes between skeletal F-actin and chicken gizzard myosin subfragments 1 (S1) were investigated by limited proteolysis and by chemical cross-linking with 1-ethyl-3-[3-(dimethyl-amino)propyl]carbodiimide. Earlier, these approaches were used to analyze the actin site on the skeletal muscle myosin heads [Mornet, D., Bertrand, R., Pantel, P., Audemard, E., & Kassab, R. (1981) Biochemistry 20, 2110-2120; Labbé, J.P., Mornet, D., Roseau, G., & Kassab, R. (1982) Biochemistry 21, 6897-6902]. In contrast to the case of the skeletal S1, the cleavage with trypsin or papain of the sensitive COOH-terminal 50K-26K junction of the head heavy chain had no effect on the actin-stimulated Mg2+-ATPase activity of the smooth S1. Moreover, actin binding had no significant influence on the proteolysis at this site whereas it abolished the scission of the skeletal S1 heavy chain. The COOH-terminal 26K segment of the smooth papain S1 heavy chain was converted by trypsin into a 25K peptide derivative, but it remained intact in the actin-S1 complex. A single actin monomer was cross-linked with the carbodiimide reagent to the intact 97K heavy chain of the smooth papain S1. Experiments performed on the complexes between F-actin and the fragmented S1 indicated that the site of cross-linking resides within the COOH-terminal 25K fragment of the S1 heavy chain. Thus, for both the striated and smooth muscle myosins, this region appears to be in contact with F-actin.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1985

Further characterization of the structural and functional properties of the cross-linked complex between F-actin and myosin S-1.

Several structural and functional properties of the covalent complex, formed upon cross-linking of the myosin heads (S-1) to F-actin with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, were characterized. The elevated Mg2+-ATPase activity was measured during a 1-month storage of the complex under various conditions. In aqueous medium it showed a rapid time-dependent decrease but it was significantly more stable in the presence of 50% ethylene glycol at -20 degrees C. The ATPase loss most likely reflects a progressive conformational change within the S-1 ATPase site resulting from its greater exposure to the medium, induced by the permanently bound F-actin. The covalent acto-S1 complex was submitted to depolymerization-repolymerization experiments using different depolymerizing agents (0.6 M KI; 4.7 M NH4Cl; low-ionic-strength solution). The depolymerization led to an immediate loss of the enhanced Mg2+-ATPase activity; this activity was almost entirely recovered upon repolymerization of the complex. The protein material formed upon depolymerization of the covalent acto-S1 was analyzed by gel chromatography, gel electrophoresis, analytical ultracentrifugation and electron microscopy. It comprised mainly small-sized actin oligomers associated with the covalently bound S-1 and only a limited amount of free G-actin. The results illustrate the relationships between the filamentous state of actin and its ability to stimulate the Mg2+-ATPase activity of S-1. They also indicate that the binding of S-1 to F-actin is transmitted to several neighbouring actin subunits and strengthens the interactions between actin monomers. Acto-S1 cross-linked complexes were prepared in the presence of tropomyosin and the tropomyosin-troponin system. Under the conditions employed, the regulatory proteins were not cross-linked to actin or S-1 and did not affect the extent or the pattern of S-1 cross-linking to F-actin. Measurements of the elevated Mg2+-ATPase activity of the cross-linked preparations revealed that tropomyosin and the tropomyosin-troponin complex, in the absence of Ca2+, inhibit ATP hydrolysis; the extent of ATPase inhibition (up to 50%) was dependent on the amount of covalently bound S-1, being larger at low level of S-1 cross-linking; the addition of Ca2+ restored the ATPase activity to the control value. The data provide direct evidence that the regulatory proteins can modulate directly the kinetics of ATP hydrolysis by the covalent acto-S1 complex as has earlier been suggested for the reversible complex [Chalovich, J. M. and Eisenberg, E. (1982) J. Biol. Chem. 257, 2432-2437].(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗
PubMed1985

[Hemodynamic evaluation of Ionescu-Shiley pericardial bioprostheses].

36 patients with a total of 39 pericardial Ionescu-Shiley bioprostheses (20 aortic, 13 mitral and 3 double valve replacements) were studied. The population consisted if 12 women and 24 men with an average age of 33 +/- 11 years. The control was performed on average 7 +/- 4 months after surgery. At the time of investigation all patients were in functional classes I or II of the NYHA. The average cardio-thoracic ratio was 0.51 +/- 0.05. The catheter data showed a mean pulmonary capillary pressure of 10 +/- 2.7 mmHg, a mean cardiac index of 3.2 +/- 0.9 l/min/m2, a mean end diastolic volume of 132 +/- 33 ml/m2 and a mean ejection fraction of 0.53 +/- 0.12. Haemodynamic data was obtained under basal conditions and during intravenous infusion of isoproterenol. The average transvalvular pressure gradient was measured by transseptal catheterisation. The cardiac output was measured by dye dilution and the functional surface area calculated using the Gorlin formula (k = 44.5 for the aortic valve and k = 31 for the mitral valve). Perivalvular leaks were excluded by selective left ventriculography or aortography. The average transvalvular pressure gradients for the aortic valve prostheses (no 19 = 1, no 21 = 4, no 23 = 3, no 25 = 7, no 27 = 8) were 17 +/- 7 mmHg for no 19 and 21, 12 +/- 5 mmHg for no 23 and 25, and 9.7 +/- 2.7 mmHg for no 27.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

[Recurrent systemic arterial embolism in patients with valve prostheses].

The first 400 cases of 1,436 patients undergoing cardiac valve replacement were analysed to determine the clinical features of recurrent systemic embolism. The average follow-up period was 87 months. Three groups of patients were compared: A: 289 cases without embolic complications (72.5 p. 100) B: 78 cases with a single systemic thrombo-embolic event. (TEE) (19,5 p. 100) C: 33 cases with recurrent TEE (8.25 p. 100). The incidence of recurrence is high (30 p. 100 of cases, 8,1 p. 100 per patient year, compared to 3.8 p. 100 for the first TEE). The site of recurrent embolism was the same in 45 p. 100 of cases. The consequences were serious, 30 to 40 p. 100 of events being associated with death or invalidating sequellae. Four factors predisposed to TEE: mitral valve prosthesis, atrial fibrillation, left atrial dilatation and poor anticoagulant control. Fifty-four months after the first TEE, 60 p. 100 with inadequate anticoagulation had a recurrence compared to 20 p. 100 of patients with satisfactory control. Twenty-six patients (Groups B and C) had operative or autopsy examination of the prosthesis: thrombosis was found in 12 out of 18 cases in Group B, and in 7 out of 8 cases in Group C. Reoperation may be necessary to change the valve (27 out of 1,436 patients). Strict adherence to anticoagulant therapy remains the best prophylaxis against TEE and their recurrence.

Adolescent↗
PubMed1984

The interaction of skeletal myosin subfragment 1 with the polyanion, heparin.

The association between chymotryptic skeletal muscle myosin subfragment 1 (S1) and the polyanion, heparin, was investigated as an experimental approach in probing the functional importance of the cationic sites on S1 and their involvement in ionic interactions within the myosin head during energy transduction. The direct binding of heparin, used at micromolar concentrations, and its influence on the structural and functional properties of S1 were followed by gel chromatography, electron microscopy, chemical cross-linking techniques and limited digestion studies. 1. The limited tryptic digestion of S1 showed that the presence of heparin, as well as of the homopolymer, poly-(L-glutamic acid) causes a specific structural change in the 50-kDa heavy chain region of S1 and accelerates the breakdown of this segment into a 45-kDa species by a proteolytic cleavage restricted to its COOH-terminal portion. Under similar experimental conditions, the binding of MgATP and MgADP to S1 led also to the 50-kDa----45-kDa conversion, suggesting that the S1-nucleotide interactions exhibit some resemblances to the polyanion-S1 binding of polyanionic ligands to S1. This particular area is adjacent to the actin site containing the 45-kDa and 20-kDa segments of the S1 heavy chain. On the other hand, the polyanions as well as nucleotides induced changes in the interface between the heavy chain and the alkali light chains. 2. Moreover, the binding of heparin to S1 resulted in the self-association of the enzyme and the production of stable small S1 oligomers, most likely dimers, which were demonstrated by the alteration of the size of the S1 particles examined by electron microscopy and their freezing by chemical cross-linking agents. These findings are relevant to the recently reported property of skeletal chymotryptic S1 to form dimers under convenient ionic conditions, in particular in the presence of Mg-nucleotides. The interaction of cationic sites on S1 and possibly on the 50-kDa region of the heavy chain with polyanions promotes the dimerization of the S1 molecules. The binding of S1 to F-actin abolished S1 aggregation.

Actins↗