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.

Relation between structure and function in some partially synthetic ribonucleases S'. Enzymic and spectroscopic investigation on [Orn10, Asn14]-RNase S' and 1epsilon, 7epsilon, 10delta-triguanidino-[Orn10, Asn14]-RNase S'

Some analogues have been prepared of S-peptide, the peptide obtained together with S-protein from subtilisn-modified beef pancreatic R Nase A. The syntheses are described of [Orn10, Asn14]-S-peptide and 1epsilon, 7epsilon, 10delta-triguanidino-[Orn10, Asn14]-S-peptide. The S-peptide analogues are able to activate S-protein at the level of the parent [Orn10]-S-peptide and 1epsilon, 7epsilon-diguanidino-S-peptide respectively, although at high peptide-to-protein molar ratios. After their recombination with S-protein the buried character of Tyr-25 was restored, as judged from difference absorption and circular dichroism spectra in the near-ultraviolet region. These findings indicate that the asparaginyl residue is a possible naturally occurring substituent in the R Nase A sequences whose state of amidation in position 14 has not yet been defined.

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.