No abstract

The structures of two pseudopolymorphs of N-acetyl-L-phenylalanine methyl ester, L-AcFOMe, were determined at both 293 (2) and 150 (2) K. At room temperature, the orthorhombic phase C(12)H(15)NO(3) (I), with space group P2(1)2(1)2(1), converts into the tetragonal phase C(12)H(15)NO(3).0.5H(2)O (II), with space group P4(1)2(1)2, in the presence of water. In the structures of both pseudopolymorphs, alternating layers of hydrophilic and hydrophobic intermolecular interaction can be distinguished. In the hydrophilic layers the structures are stabilized by moderate hydrogen bonds of the type N-H...O for the anhydrous L-AcFOMe and of types N-H...O and O-H...O for the hemihydrate. Weak C-H...pi interactions are observed within the hydrophobic layers: for (I) they are of type III [Malone et al. (1997). J. Chem. Soc. Faraday Trans. 93, 3429-3436], whereas typical type I edge-to-face interactions are present for (II). The differences between the hydrogen-bonding networks of (I) and (II) are discussed in terms of graph-set analysis.

The crystal structure of a protected L-tyrosine, namely N-acetyl-L-tyrosine methyl ester monohydrate, C(12)H(15)NO(4).H(2)O, was determined at both 293 (2) and 123 (2) K. The structure exhibits a network of O-H...O and N-H...O hydrogen bonds, in which the water molecule plays a crucial role as an acceptor of one and a donor of two hydrogen bonds. Molecules of water and of the protected L-tyrosine form hydrogen-bonded layers perpendicular to [001]. C-H...pi interactions are observed in the hydrophobic regions of the structure. The structure is similar to that of N-acetyl-L-tyrosine ethyl ester monohydrate [Soriano-García (1993). Acta Cryst. C49, 96-97].

In order to reveal the possible mechanism of the recognition of antiarrhythmic agents class I and class III by the amino acid residues, which are responsible for drug binding to the selectivity filters either in the sodium or potassium ion channels, co-crystallizations of procainamide hydrochloride and N-acetylprocainamide hydrochloride with N-acetyl-L-tyrosine methyl ester and N-acetyl-L-phenylalanine methyl ester were performed using various conditions. Because the crystallization of the complexes failed, the intermolecular interactions between the components were evidenced using NMR spectroscopy. Exclusively, in the case of N-acetylprocainamide hydrochloride and N-acetyl-L-tyrosine methyl ester, two-dimensional NMR experiments and Job Plot analysis indicated the formation of the 1:1 complex in DMSO-d 6 solution (with the association constant of 16 M -1 ), whereas for the mixture of procainamide hydrochloride with N-acetyl-Ltyrosine methyl ester, the complex formation was not confirmed. The NMR results were discussed using crystal structure data obtained for N-acetylprocainamide hydrochloride, procainamide hydrochloride, as well as procainamide dihydrochloride, and were compared with the known pharmacological activity of the antiarrhythmic agents.

1 ms. This improved time resolution reveals three populations of acto-myosin attachments with lifetimes that differ by more than 10-fold, likely representing three different biochemical and/or mechanical states. The slowest of these rates is ATP dependent at low MgATP concentrations and corresponds well with the expected rate of ATP-induced dissociation. The populations with shorter lifetimes likely represent dissociation from actomyosin states that precede ATPinduced dissociation. The force dependence of these lifetimes and the relative amplitude of each phase reveal information about mechano-chemical transitions in cardiac myosin that have not previously been probed in the single molecule regime. In addition, ensemble averages of individual attachment events reveal the amplitude and timing of both sub-steps of b-cardiac myosin's power stroke. Through these ensemble averages, we can separately resolve the prepowerstroke/actin-bound state and the post-powerstroke state, representing the first single-molecule observation of the initial actin displacement by cardiac myosin under load. Myosins are proposed to utilize a conserved structural mechanism to generate force in which small conformational changes in the active site result in a large swing of the lever arm or light chain binding region. The converter domain is a flexible region that provides a link between the catalytic domain and lever arm and is proposed to play a critical role in the allosteric communication between these two domains. We introduced the R712G mutation in the converter domain and examined the impact of this mutation on the structural and functional properties of myosin V. The mutation resulted in a 16% reduction in the maximum actin-activated ATPase rate and no change in the actin concentration at which the ATPase activity is one-half maximal (KATPase). The sliding velocities examined in the in vitro motility assay were very similar between WT and R712G MV. We have developed a novel FRET system in myosin V (MV) that allows examination of the dynamics of lever arm motion. We labeled MV 11IQ containing an N-terminal (NT) tetracysteine motif with the bisarsenical dye FlAsH (MV.NT.FlAsH). The first IQ motif of MV.NT.FlAsH was exchanged with QSY-9 labeled CaM, a non-fluorescent acceptor. We followed the motion of the lever-arm during the ATP binding (recovery stroke) and actinactivated product release (power stroke) steps using stopped-flow FRET. The R712G mutation reduced the rate of the recovery stroke by 23% while having little impact on the fast power stroke that occurs prior to phosphate release. Thus, a mutation in the converter domain can specifically impact the recovery stroke without altering the power stroke demonstrating different allosteric mechanisms are responsible for these two key structural transitions. 1511-Pos Board B462Myosin Steps Symmetrically along Actin Myosin 5a is a homodimer belonging to the family of processive molecular motors that transform chemical energy into directional motion along the cytoskeleton network. Despi...