The molecular chaperone Hsp27 exists as a distribution of large oligomers that are disassembled by phosphorylation at Ser-15, -78, and -82. It is controversial whether the unphosphorylated Hsp27 or the widely used triple Ser-to-Asp phosphomimic mutant is the more active molecular chaperone in vitro. This question was investigated here by correlating chaperone activity, as measured by the aggregation of reduced insulin or ␣-lactalbumin, with Hsp27 self-association as monitored by analytical ultracentrifugation. Furthermore, because the phospho-mimic is generally assumed to reproduce the phosphorylated molecule, the size and chaperone activity of phosphorylated Hsp27 were compared with that of the phospho-mimic. Hsp27 was triply phosphorylated by MAPKAP-2 kinase, and phosphorylation was tracked by urea-PAGE. An increasing degree of suppression of insulin or ␣-lactalbumin aggregation correlated with a decreasing Hsp27 self-association, which was the least for phosphorylated Hsp27 followed by the mimic followed by the unphosphorylated protein. It was also found that Hsp27 added to pre-aggregated insulin did not reverse aggregation but did inhibit these aggregates from assembling into even larger aggregates. This chaperone activity appears to be independent of Hsp27 phosphorylation. In conclusion, the most active chaperone of insulin and ␣-lactalbumin was the Hsp27 (elongated) dimer, the smallest Hsp27 subunit observed under physiological conditions. Next, the Hsp27 phospho-mimic is only a partial mimic of phosphorylated Hsp27, both in self-association and in chaperone function. Finally, the efficient inhibition of insulin aggregation by Hsp27 dimer led to the proposal of two models for this chaperone activity.

Polyethylene, water, lithium fluoride, aluminium, and sulfur targets have been irradiated with 1-GeV bremsstrahlung beams at the Frascati electron synchrotron and the yields of some spallatjon products from Al and S and of C and VBe from C, 60, 9F, Al, and S have been measured by the induced-activity and radiochemical methods. Evidence has been deduced for fragmentation from the mass-yield distribution of the photoproduced nuclides in 27Al and S

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A semi-empirical four-parameter formula is proposed in order to systematize intermediate-and high-energy proton-induced spallation yields of target nuclei covering the 50-100 mass number interval. It is shown that the measured yields are reproduced by the formula with a degree of accuracy which is comparable with or better than those obtained in previous proton-spallation systematics by other authors. The formula predicts reliable values for the most probable mass number of isotopie distributions. In addition, it allows one to derive in a simple way the mean nominal number of nucléons lost by the struck target nucleus, the chargeand mass-yield distributions for the spallation residuals, the total spallation reaction cross section, and the N/Z charge-dispersion curves.