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At least 1,045 records · Page 58Linked to original sources
PubMed2006

Valine-based biphenylsulphonamide matrix metalloproteinase inhibitors as tumor imaging agents.

Among matrix metalloproteinases (MMPs), the subfamily of gelatinases (MMP-2, MMP-9) is of particular interest due to their ability to degrade type IV collagen and other non-fibrillar collagen domains and proteins such as fibronectin and laminin. Whilst malignant cells often over-express various MMPs, the gelatinases have been most consistently detected in malignant tissues and associated with tumor growth, metastatic potential and angiogenesis. Radiosynthesis of carboxylic (1') and hydroxamic (2') MMPIs resulted in radiochemical yields of 70 +/- 5% (n = 6) and 60 +/- 5% (n = 4), respectively. Evaluation in A549-inoculated athymic mice showed a tumor uptake of 2. 0+/- 0.7%ID/g (3 h p.i.), a tumor/blood ratio of 0.5 and a tumor/muscle ratio of 4.6 at 48 h p.i. for 1'. For compound 2' a tumor uptake of 0.7 +/- 0.2%ID/g (3 h p.i.), a tumor/blood ratio of 1.2 and a tumor/muscle ratio of 1.8 at 24 h p.i. were observed. HPLC analysis of the blood (plasma) showed no dehalogenation or other metabolites of 1' 2 h p.i. For compound 2', 65.4% of intact compound was found in the blood (plasma) and one polar metabolite (31%) was detected whereas in the tumor 91.8% of the accumulated activity was caused by intact compound and only 8.1% by the metabolite. Planar imaging, using a Toshiba GCA-9300A/hg SPECT camera, showed that tumor tissue could be visualized and that image quality improved by decreasing specific activity resulting in lower liver uptake, indicating some degree of saturable binding in the liver. In vivo evaluation of these radioiodinated carboxylic and hydroxamic MMP inhibitor tracers revealed that MMP inhibitors could have potential as tumor imaging agents, but that further research is necessary.

Animals↗
PubMed2004

Importance of valine 567 in substrate recognition and oxidation by neuronal nitric oxide synthase.

Nitric oxide (NO) is synthesised by a two-step oxidation of -arginine (L-Arg) in the active site of nitric oxide synthase (NOS) with formation of an intermediate, N omega-hydroxy-L-Arg (NOHA). Crystal structures of NOSs have shown the importance of an active-site Val567 residue (numbered for rat neuronal NOS, nNOS) interacting with non-amino acid substrates. To investigate the role of this Val residue in substrate recognition and NO-formation activity by nNOS, we generated and purified four Val567 mutants of nNOS, Val567Leu, Val567Phe, Val567Arg and Val567Glu. We characterized these proteins and tested their ability to generate NO from the oxidation of natural substrates L-Arg and NOHA, and from N-hydroxyguanidines previously identified as alternative substrates for nNOS. The Val567Leu mutant displayed lower NO formation activities than the wild type (WT) in the presence of all tested compounds. Surprisingly, the Val567Phe mutant formed low amounts of NO only from NOHA. These two mutants displayed lower affinity for L-Arg and NOHA than the WT protein. Val576Glu and Val567Arg mutants were much less stable and did not lead to any formation of NO. These results suggest that Val567 is an important residue for preserving the integrity of the active site, for substrate binding, and subsequently for NO-formation in nNOS.

Amino Acid Substitution↗
PubMed1999

Thermodynamics and kinetics of a folded-folded' transition at valine-9 of a GCN4-like leucine zipper.

Spin inversion transfer (SIT) NMR experiments are reported probing the thermodynamics and kinetics of interconversion of two folded forms of a GCN4-like leucine zipper near room temperature. The peptide is 13Calpha-labeled at position V9(a) and results are compared with prior findings for position L13(e). The SIT data are interpreted via a Bayesian analysis, yielding local values of T1a, T1b, kab, kba, and Keq as functions of temperature for the transition FaV9 right arrow over left arrow FbV9 between locally folded dimeric forms. Equilibrium constants, determined from relative spin counts at spin equilibrium, agree well with the ratios kab/kba from the dynamic SIT experiments. Thermodynamic and kinetic parameters are similar for V9(a) and L13(e), but not the same, confirming that the molecular conformational population is not two-state. The energetic parameters determined for both sites are examined, yielding conclusions that apply to both and are robust to uncertainties in the preexponential factor (kT/h) of the Eyring equation. These conclusions are 1) the activation free energy is substantial, requiring a sparsely populated transition state; 2) the transition state's enthalpy far exceeds that of either Fa or Fb; 3) the transition state's entropy far exceeds that of Fa, but is comparable to that of Fb; 4) "Arrhenius kinetics" characterize the temperature dependence of both kab and kba, indicating that the temperatures of slow interconversion are not below that of the glass transition. Any postulated free energy surface for these coiled coils must satisfy these constraints.

Amino Acid Sequence↗
PubMed2002

Apisimin, a new serine-valine-rich peptide from honeybee (Apis mellifera L.) royal jelly: purification and molecular characterization.

A peptide named apisimin was found in honeybee (Apis mellifera L.) royal jelly (RJ). N-terminal sequencing showed that this peptide corresponded to the sequence of a cDNA clone isolated from an expression cDNA library prepared from heads of nurse honeybees. No homology was found between the protein sequence of apisimin with a molecular mass of 5540.4 Da and sequences deposited in the Swiss-Prot database. The 54 amino acids of apisimin do not include Cys, Met, Pro, Arg, His, Tyr, and Trp residues. The peptide shows a well-defined secondary structure as observed by CD spectroscopy, and has the tendency to form oligomers. Isoelectrofocusing showed apisimin to be an acidic peptide.

Amino Acid Sequence↗
PubMed2003

A point mutation of valine-311 to methionine in Bacillus subtilis protoporphyrinogen oxidase does not greatly increase resistance to the diphenyl ether herbicide oxyfluorfen.

In an effort to asses the effect of Val311Met point mutation of Bacillus subtilis protoporphyrinogen oxidase on the resistance to diphenyl ether herbicides, a Val311Met point mutant of B. subtilis protoporphyrinogen oxidase was prepared, heterologously expressed in Escherichia coli, and the purified recombinant Val311Met mutant protoporphyrinogen oxidase was kinetically characterized. The mutant protoporphyrinogen oxidase showed very similar kinetic patterns to wild type protoporphyrinogen oxidase, with slightly decreased activity dependent on pH and the concentrations of NaCl, Tween 20, and imidazole. When oxyfluorfen was used as a competitive inhibitor, the Val311Met mutant protoporphyrinogen oxidase showed an increased inhibition constant about 1.5 times that of wild type protoporphyrinogen oxidase. The marginal increase of the inhibition constant indicates that the Val311Met point mutation in B. subtilis protoporphyrinogen oxidase may not be an important determinant in the mechanism that protects protoporphyrinogen oxidase against diphenyl ether herbicides.

Amino Acid Sequence↗