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The guanidine hydrochloride induced unfolding of the heat shock protein DnaK was studied using flourescence, size-exclusion HPLC, circular dichroism and dynamic light scattering. The denaturation process was noted to occur in two stages with one expandable intermediate state in between. The first stage was influenced by the presence of Mg/ADP or Mg/ATP although the next transition was unaffected by nucleotides. Thus, a hierarchical system of unfolding was suggested to characterize the denaturation of DnaK.

Hsp60 and Hsp70, the molecular chaperone proteins, bind themselves to short peptides and unfolded proteins when twisted in the cell functions under stress induced and normal conditions. The disintegration of the substrate polypeptides from the chaperone is caused by the addition of Mg-ATP, and occurs since the ATP analogue is not capable of replacing ATP. The disintegration Hsp 70-substrate proteins require the hydrolysis of the Mg-ATP in addition to the earlier mentioned reactions. Mg-ATP binding is more essential than the Mg-ATP hydrolysis to the disintegration of the molecular chaperone proteins.

Escherichia coli cold shock protein, CspA, folds very rapidly (time constant, τ = 4 msec) by an apparent two-state mechanism. However, recent time-resolved infrared (IR) temperature-jump experiments indicate that the folding trajectory of CspA may be more complicated. The sole tryptophan of wild-type CspA (Trp11), which is used to monitor the folding process by fluorescence spectroscopy, is located in an unusual aromatic cluster on the surface of CspA within the nucleic acid binding site. To gain a more global picture of the folding kinetics of CspA and to determine if there are any previously undetected intermediates, we have introduced a second tryptophan at three different surface locations in the protein. The three mutations did not significantly alter the tertiary structure of CspA, although two of the substitutions were found to be slightly stabilizing. Two-state folding, as detected by stopped-flow fluorescence spectroscopy, is preserved in all three mutants. These results indicate that the fast folding of CspA is driven by a concerted mechanism. [ABSTRACT FROM AUTHOR]

We show that the photoionization dynamics of a small excited polyatomic molecule can be partially elucidated from the measurement of photoelectron angular distributions (PADs) at an energy resolution of only around 20 meV following excitation of various selected rotational levels in an excited electronic state. To illustrate this we present PADs corresponding to the formation of vibrationally resolved NH[sub 3][sup +] following the excitation of NH[sub 3] to selected rotational levels in its B˜ [sup 1]E[sup ″] electronic state. We also present a preliminary time-of-flight photoelectron spectrum showing peaks corresponding to resolved rotational levels of the NH[sub 3][sup +] ion. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this study, members of a professional opera chorus were recorded using close microphones, while singing in both choral and solo modes. The analysis included computation of long-term average spectra (LTAS) for the two song sections performed and calculation of singing power ratio (SPR) and energy ratio (ER), which provide an indication of the relative energy in the singer's formant region. Vibrato rate and extent were determined from two matched vowels, and SPR and ER were calculated for these vowels. Subjects sung with equal or more power in the singer's formant region in choral versus solo mode in the context of the piece as a whole and in individual vowels. There was no difference in vibrato rate and extent between the two modes. Singing in choral mode, therefore, required the ability to use a similar vocal timbre to that required for solo opera singing.