Micellar Solubilization of Proteins in Aprotic Solvents and their Spectroscopic Characterisation

The quaternary ammonium salt methyl-trioctylammonium chloride enables the transfer of α-chymotrypsin, trypsin, pepsin and glucagone from water to cyclohexane. Reversed micelles, whose polar core solubilizes both protein and water, are probably formed in the apolar phase. The influence of various parameters on the phase transfer (concentration, pH, solvent, temperature, etc.) has been investigated. Absorption, fluorescence and circular dichroism studies of the biopolymers in the cyclohexane system have been carried out. For trypsin and chymotrypsin, the CD. signal in the 200 nm region is very similar in water and in cyclohexane, which suggests that the polypeptide folding is not substantially different in the two phases. The fluorescence quantum yield is always much larger in the cyclohexane phase than in water. The longer wavelength region of the UV. absorption spectrum is slightly red-shifted relative to water, and a band at 225 nm, probably arising from the aromatic chromophore, is apparent in the organic phase. Reasons for these spectral perturbations are discussed. The enzymes transferred from water into cyclohexane phases can be continuously retransferred into a second water phase. The possible relevance of this ‘double transfer’ as a model for the vectorial transport of biopolymers or a separation technique is discussed.     

Electrochemical behaviour of 1-benzyl-3-carbamoylpyridinium chloride,a NAD+ model compound

In aqueous media, 1-benzyl-3-carbamoylpyridinium ion undergoes an initially reversible one-electron reduction to produce a free radical, which irreversibly dimerises to a 4,4′-linked diastereoisomeric pair. At more negative potential, the free radical undergoes a further one-electron reduction to a mixture of 1,6- and 1,4-dihydropyridine derivatives. At sufficiently positive potential the dimers can be oxidised back to pyridinium cation. The dimeric products are strongly adsorbed on the electrode surface, also at potential values where 2e products are formed, and this is a preparative drawback for the dimers and the dihydropyridines. Such problems can be overcome by the addition of benzene and of surface-active substances respectively. A detailed mechanism of the electrochemical reduction of 1-benzyl-3-carbamoylpridinium ion is proposed.     

Sui fenomeni giroscopici

Sunto. Scritte le equazioni dinamiche del solido con punto fisso in forma ? assiale ?, si definiscono diversi tipi di effetti giroscopici per un asse qualunque del corpo; si precisano le condizioni perchè sussistano tali effetti e si ricavano cosí in forma classica, ma con procedimento nuovo, vari risultati vecchi e nuovi. A Dario Graffi nel suo 70^o compleanno Entrata in Redazione il 3 marzo 1975. Lavoro eseguito nell'ambito dell'attività dei Raggruppamenti di ricerca matematica del C.N.R.     

Stabilità delle soluzioni di disequazioni variazionali ellittiche e paraboliche quasi lineari

Riassunto In questo lavoro, si studia, per una classe di operatori quasi-lineari, il problema della dipendenza simultanea dai vincoli, dai coefficienti dell'operatore e dai termini noti delle soluzioni di disequazioni variazionali ellittiche e delle soluzioni forti di disequazioni variazionali paraboliche. L'esistenza di queste ultime è consequenza dei risultati precedenti.

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Summary We study the problem of the dependence from the data of the solutions of quasilinear elliptic variational inequalities. We also consider the case of the strong solutions of parabolic variational inequalities, whose existence has been proved as a consequence of the previous results.

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Lavoro eseguito nell'ambito del G.N.A.F.A.—C.N.R.     

On correlation function methods for detecting the stochastic transition

The use of correlation function methods to predict the onset of chaotic motion in conservative Hamiltonian systems is critically examined. It is shown that microcanonical correlation functions do not, in general, provide a convenient criterion to distinguish between stable and unstable motions.     

A GAP-GTPase-GDP-Pi Intermediate Crystal Structure Analyzed by DFT Shows GTP Hydrolysis Involves Serial Proton Transfers

Cell signaling by small G proteins uses an ON to OFF signal based on conformational changes following the hydrolysis of GTP to GDP and release of dihydrogen phosphate (P_i). The catalytic mechanism of GTP hydrolysis by RhoA is strongly accelerated by a GAP protein and is now well defined, but timing of inorganic phosphate release and signal change remains unresolved. We have generated a quaternary complex for RhoA-GAP-GDP-P_i. Its 1.75 Å crystal structure shows geometry for ionic and hydrogen bond coordination of GDP and P_i in an intermediate state. It enables the selection of a QM core for DFT exploration of a 20 H-bonded network. This identifies serial locations of the two mobile protons from the original nucleophilic water molecule, showing how they move in three rational steps to form a stable quaternary complex. It also suggests how two additional proton transfer steps can facilitate P_i release.     

Filling factor dependence of the fractional quantum Hall effect gap

We directly measure the chemical potential jump in the low-temperature limit when the filling factor traverses the nu=1/3 and nu=2/5 fractional gaps in two-dimensional (2D) electron system in GaAs/AlGaAs single heterojunctions. In high magnetic fields B, both gaps are linear functions of B with slopes proportional to the inverse fraction denominator, 1/q. The fractional gaps close partially when the Fermi level lies outside. An empirical analysis indicates that the chemical potential jump for an ideal 2D electron system, in the highest accessible magnetic fields, is proportional to q(-1) B(1/2).