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B Filippi

Publications and source records attributed to B Filippi.

At least 37 records · Page 2Linked to original sources
PubMed1983

Synthesis of N alpha-, and C alpha-derivatives of (D)Ala2, Leu5-enkephalin.

Some (D)Ala2, Leu5-Enkephalin derivatives containing hydrophilic or hydrophobic moieties have been synthesized by the solution method. Improvement in the analgesic effect was achieved by increasing the hydrophilicity of the parent compound through covalent linkage of the 2-deoxy-D-glucopyranosyl residue to the carboxyl terminal amide nitrogen of leucine 5. Reductive glucosamination of (D)Ala2, Leu5-Enkephalin practically abolishes activity and increase in hydrophobicity lowers the potency of the parent compound in both the in vitro and in vivo tests.

Analgesics↗
PubMed1982

Effects of pH and urea on the conformational properties of subtilisin DY.

Subtilisin DY is very resistant to the denaturing action of urea: the conformational properties are not affected up to 4.5 M-urea, and even in the presence of 8 M-urea there is only a slow loss of ordered structure and caseinolytic activity. C.d. and fluorescence-emission studies also show that this proteinase is stable in the 5.5-10.0 pH range, whereas below pH 5.5 a sharp denaturation occurs that is complete at pH 4.5. Protein denaturation leads to a change of the emission quantum yield; in particular, in the native protein, indole fluorescence is quenched by some amino groups. Moreover, subtilisin DY possesses two classes of tyrosine residues: one class of exposed residues titrates normally, with pKapp. = 10.24, whereas one class of partially buried or hydrogen-bonded residues ionizes with pKapp. = 11.58. In general, such conformational properties resemble those of other subtilisins. However, some differences occur: e.g., subtilisin DY is less stable at acidic pH values and its tyrosine residues are more accessible to the solvent. Such differences are probably due to small variations of the three-dimensional structure; e.g., subtilisin DY has a slightly lower alpha-helix content.

Bacillus subtilis↗
PubMed1980

Inhibition of the cytochrome c/cytochrome c oxidase system by cytochrome c derivatives and related fragments.

The oxidation of ferrocytochrome c mediated by cytochrome c oxidase was investigated in the presence of ferricytochrome c, trifluoroacetyl-cytochrome c, the heme fragments Hse65-[1-65] and Hse80-[1-80] and their respective porphyrin derivatives, as well as carboxymethylated apoprotein and related fragments, polycations, salts and neutral additives. The inhibition of the redox reaction by salts and neutral molecules, even if in theoretical agreement with their effect on electrostatic interactions, may alternatively be interpreted in terms of hydrophobicity. The latter can account for the inhibitory properties of trifluoroacetylated ferricytochrome c, similar to those of ferricytochrome c. On the assumption that the inhibitory properties of some of the investigated derivatives monitor their binding affinities to the cytochrome c oxidase at the cytochrome c binding sites, the experimental results do not confirm a primarily electrostatic character for the cytochrome c/cytochrome c oxidase association process. Strong indication was found that the cytochrome c C-terminal sequence is critically involved in the complex formation. Conformational studies by circular dichroism measurements and IR spectroscopy in solution and in solid state respectively, show that some of the derivatives examined may possibly acqkuire in the binding process to the oxidase, as secondary structure similar to that present in the native cytochrome c.

Amino Acids↗
PubMed1979

Protamines. II. Circular dichroism study of the three main components of clupeine.

The three main components YI, YII, and Z of clupeine, a protamine from herring, have been purified and characterized. The conformational preferences of clupeines have been examined as a funciton of pH, temperature, added salts, and presence of structure-disrupting agents and helix-supporting solvents using circular dichroism. It was found that these small basic proteins assume predominantly an unordered conformation in aqueous solution. Addition of counter ions, in particular perchlorate, and 2-chloroethanol induces in various amounts the onset of the right-handed alpha-helical conformation. Urea favors the statistical coil state. It was also demonstrated that in the 0.1--4.0 . 10(-1) M range, in contrast to clupeines YI and Z, the circular dichroic properties of the YII component do not seem to be sensitive to the addition of mono- and diphosphate.

Amino Acids↗
PubMed1979

Synthetic enkephalins. Addicting properties and conformational studies in solution.

The addicting properties of [Leu5]enkephalin in mice are conserved in the LSer3 analogue and lost both in the L-Ser2 analogue and in all the L-Cha4 derivatives of the above peptides. Fluorescence measurements in water show the presence of hydrogen-bonded tyrosul OH groups in [Leu5]-enkephalin and in its LSer2 analogue. The Phe4/Cha replacements do not influence these equilibria, but they affect the near u.v. dichroism of the hydrogen bonded tyrosyl residues. In the peptide absorption region in water solution, only [Leu5]-enkephalin and its cyclohexylalnyl derivative show a positive dichroism towards high frequencies, which is maintained in 8 M ura. No clear relation is found between conformation(s) in solution and biological activity. A II' beta-turn, with residues in positions 2 and 3 at the corners, is suggested for the conformation of enkephalin bound to the receptors involved in the bioassay here used.

Amino Acid Sequence↗
PubMed1979

Protamines. III. Synthesis of the tetradecapeptide corresponding to the C-terminal sequence 52--65 of galline.

The synthesis of peptides containing blocks of arginyl residues is proposed through amidination of the corresponding ornithyl analogs. In order to test this strategy the ornithyl analog of the C-terminal sequence 52--65 of galline was synthesized by the conventional method. The amidination reaction, performed on fragments of different length and ornithyl-residue content, quantitatively converts ornithines into arginines. The strategy proposed may represent a powerful tool for the synthesis of protamines and other basic proteins.

Amidines↗
PubMed1977

Kinetic and conformational studies on some partially synthetic ribonuclease S' analogues modified in position 8.

Syntheses are described of two S-peptide analogues where the arginyl residue in position 10 has been replaced by ornithine and the phenylalanine in position 8 has been substituted by the unnatural amino acids cyclohexylalanine or p-fluorophenylalanine. In order to regenerate the arginyl residue, which is present in position 10 in the natural sequence, the S-peptide analogues beloning to the [Orn10]-series are transformed into the corresponding guanidinated derivatives by treatment with O-methylisourea. 1epsilon, 7epsilon, 10delta triguan-[Cha8, Orn10]-, 1epsilon, 7epsilon, 10delta-triguan-[pF-Phe8, Orn10]- and 1epsilon, 7epsilon, 10delta-triguan-[Tyr8, Orn10]-S-peptides were prepared. The ability to bind to and activate the S-protein of the synthetic S-peptide analogues, before and after guanidination, was tested by exploring their capacity to generate ribonuclease activity using RNA and C greater than p as substrates. The affinity of the different peptides for the S-protein in the absence of substrate was evaluated by difference spectroscopy.

Amino Acid Sequence↗
PubMed1977

Studies on cytochrome C. XII. Synthesis of the protected undecapeptide (sequence 66-76) and pentadecapeptide (sequence 66-80) of horse heart cytochrome c.

This paper is part of a series on synthesis of suitably protected peptides covering the 66-104 sequence of horse heart cytochrome c. It describes the preparation, by conventional procedures, of a partially protected N alpha-benzyloxycarbonyl-undecapeptide hydrazide corresponding to the sequence from 66 to 76 (Fragment F), which represents a building block for the synthesis of the entire 66-104 sequence. Moreover, the preparation is described of a partially protected pentadecapeptide corresponding to the sequence region 66 to 80, which represents the key peptide for the semisynthesis of the same COOH-terminal sequence utilizing the natural 81-104 N epsilon-trifluoroacetylated CNBr fragment.

Amino Acid Sequence↗
PubMed1977

Studies on cytochrome c. XIV. Synthesis of the protected heptadecapeptide (sequence 88-104) of horse heart cytochrome c.

A solution synthesis is described of the partially protected N alpha-benzyloxycarbonylheptadecapeptide Z-Lys (Tfa)-Thr-Glu-Arg-Glu-Asp-Leu-Ile-Ala-Tyr-Leu-Lys (Tfa)-Lys (Tfa)-Ala-Thr-Asn-Glu (OBu t)-OBu t corresponding to sequence 88-104 of horse heart cytochrome c. The synthesis is achieved through the preparation of two subunits H1 (sequence 88-96) and H2 (sequence 97-104) and their linkage by an azide coupling step.

Amino Acid Sequence↗
PubMed1976

Near-ultraviolet difference absorption and circular dichroism studies on partially synthetic ribonucleases S'.

Near-ultraviolet difference absorption and circular dichroism (CD) spectra were recorded upon recombination of synthetic S-peptide analogs, i.e. 1epsilon, 7epsilon-diguanidino-[Tyr8]-,1epsilon,7epsilon-diguanidono-[Asn14]-, [Phe(F)8, Orn10]- and 1epsilon, 7epsilon-diguanidino-S-peptide, with S-protein. Environmental alterations of Phe-8 in the S-peptide and Tyr-25 in the S-protein, derived from the association process, lead to strong optical signals whose location and magnitude were clearly defined by means of a comparative analysis of the above spectra. Additionally, the spectroscopic effects resulting from insertion of a tyrosyl residue into an hydrophobic environment in the presence or absence of hydrogen-bonding partners were identified and compared with similar findings obtained from the model compound p-cresol.

Circular Dichroism↗
PubMed1976

Far-ultraviolet difference absorption and circular dichroism studies on partially synthetic ribonucleases S'.

Far-ultraviolet difference absorption and circular dichroism (CD) spectra were recorded upon recombination of synthetic S-peptide analogs, i.e. 1epsilon, 7epsilon-diguanidino-[Tyr8]-, 1epsilon, 7epsilon-diguanidino-[Asn14]-, [Phe(F)8, Orn10]-, [Cha8, Orn10]- and 1epsilon, 7epsilon-diguanidono-S-peptide, with S-protein. The aromatic chromophores contributions to the absorption spectra in the 220-250 nm wavelengths interval strongly exceed the hyperchromism due to the random coil to right handled alpha-helix transition of the S-peptide, accompanying the association process. Contributions resulting from peptide transitions constitute a large portion of the total dichroism, nevertheless substitution of the non aromatic cycloexylalanine residue in position 8 of the S-peptide with phenylalanine, p-fluorophenylalanine and tyrosine leads to CD negative maxima located at 215, 215 and 212,5 nm, respectively. The strongest ellipticity increment (28%), relative to that of the Cha-derivative, was observed at 212,5 nm for the [Tyr8]-S-peptide analog, while in the narrow 222 nm range minimal differences were found upon insertion into the position 8 of the S-peptide of the above aromatic residues. Information derived from above data and from a comparison of RNAase A, S and S-protein CD spectra enabled us to assign the positive CD band at 240 nm in RNAase A spectrum to transitions of phenylalanines and inaccessible tyrosines.

Circular Dichroism↗