The mutual interference between the second-derivative bands of tyrosine and tryptophan in proteins has been evaluated in terms of the ratio r between two peak to peak distances. The r values have been found to be not only related to the tyrosine/tryptophan ratio but also dependent on the polarity of the medium in which tyrosyl residues are embedded. The results obtained on purified proteins have been found consistent with the available X-ray information and with the existing solvent perturbation data.

By improving glucose and lipid metabolism and reducing lipid peroxidation, carvedilol may offer advantages in patients with diabetes and hypertension.

The protein SV-IV, a major protein secreted from the rat seminal vesicle epithelium, is a basic protein with immunomodulatory, anti-inflammatory, and procoagulant activity. Predictions suggested that this protein is very flexible, with its three tyrosyl residues presumably located in water-exposed segments of the primary structure. The solution behaviour of the protein was investigated by two types of spectroscopic techniques. Modifications of the spectral characteristics of tyrosyl residues induced by changes of protein concentration were demonstrated by absorption and fluorescence experiments. In addition, secondary structure rearrangements associated with a possible self-association equilibrium were highlighted by far-UV CD spectra. The equilibrium, confirmed by chromatographic techniques, appears to control some biological properties of the protein.

We have compared the X-ray structures of 13 thermophilic proteins with their mesophilic homologues, in order to bring out differences in the stability of helices. The energy terms of a helix-coil transition algorithm were used to evaluate helix stability. Helices of thermophilic proteins are more stable than the mesophilic homologues in 69% of cases. This is due mainly to intrinsic helical propensities of amino acids, whereas minor effects are linked to main chain H-bonds, side chain-side chain interactions, capping motifs and charge-dipole effects. Furthermore, the frequency of 10 helix stabilizing factors recognized by appropriate sequence patterns was evaluated. The only factor occurring significantly in the thermostable proteins was the lack of beta branched residues. Other factors do not show a definite trend, although their occurrence in proteins is believed to be important for stability. This is discussed in the light of protein engineering applications.

We have synthesized both free and terminally-blocked peptide corresponding to the second helical region of the globular domain of normal human prion protein, which has recently gained the attention of structural biologists because of a possible role in the nucleation process and fibrillization of prion protein. The profile of the circular dichroism spectrum of the free peptide was that typical of alpha-helix, but was converted to that of beta-structure in about 16 h. Instead, below 2.1 x 10(-5) M, the spectrum of the blocked peptide exhibited a single band centered at 200 nm, unequivocally associated to random conformations, which did not evolve even after 24 h. Conformational preferences of this last peptide have been investigated as a function of temperature, using trifluoroethanol or low-concentration sodium dodecyl sulfate as alpha- or beta-structure inducers, respectively. Extrapolation of free energy data to zero concentration of structuring agent highlighted that the peptide prefers alpha-helical to beta-type organization, in spite of results from prediction algorithms. However, the free energy difference between the two forms, as obtained by a thermodynamic cycle, is subtle (roughly 5-8 kJ mol(-1) at any temperature from 280 K to 350 K), suggesting conformational ambivalence. This result supports the view that, in the prion protein, the structural behavior of the peptide is governed by the cellular microenvironment.