A rapid sensitive method for the quantification of in vitro HIV-protease activity has been developed on the basis of the endoproteolytic conversion of N-Dns-SQNYPIV to N-Dns-SQNY. The use of the N-dansyl group as a fluorescence label was shown to not significantly alter the apparent kinetic parameters for the peptideenzyme interaction. Using fluorescence detection, the dansylated product and unconverted substrate are detected in a single rapid (3 min) isocratic reverse-phase HPLC separation in quantities as low as 0.2 pmol. The method is highly reproducible and suited to a variety of applications including the analysis of large sample numbers and rigorous enzymological studies.

A study of the magnetic and magnetoelastic properties in the paramagnetic range is presented for DySb. From the analysis of magnetization curves, the existence of a two-ion magnetoelastic coupling appears as quite probable in connection with the anisotropic nature of the bilinear exchange. From the shortcomings of the mean field theory, fluctuations seem to occur, having strong magnetoelastic correlations with the lattice. Thus the first-order character of the magnetic transition results from a complex balance between various interactions.