ABSTRACT
Picosecond acoustic interferometry was used to study the acousto-optic properties of a distributed Bragg reflector (DBR) manufactured from two immiscible polymers (cellulose acetate and polyvinylcarbyzole). Picosecond strain pulses were injected into the structure and changes in its reflectance were monitored as a function of time. The reflectance exhibited single-frequency harmonic oscillations as the strain pulse traversed the DBR. A transfer matrix method was used to model the reflectance of the DBR in response to interface modulation and photo-elastic effects. This work shows that photo-elastic effects can account for the acousto-optic response of DBRs with acoustically matched layers.
ABSTRACT
The in vitro inhibition of hydroxymethylbilane synthase (EC 4.3.1.8, uroporphyrinogen I synthetase) obtained from livers of Sprague-Dawley rats has been studied with a wide range of di- and tri-valent metal ions. After purification by cell lysis, heat treatment, and centrifugation, the stable, soluble enzyme yielded sigmoidal inhibition curves with increasing concentrations of each of the 16 test ions. Using the negative logarithm of metal concentration for 50% inhibition (the pM50 value), the metal ions could be classified according to their Klopman hardness values. Very soft ions including Hg2+, intermediate ions including Cr3+, and very hard ions including Al3+ all yielded large pM50 values indicating strong inhibition. In comparison to known metal-ion chemical behaviour, these three ions could indicate three different types of inhibitory binding sites at or near the active site: Hg2+ corresponding to sulfur in cysteine, Cr3+ corresponding to nitrogen in histidine, and Al3+ corresponding to oxygen in carboxyl groups. The presence of the first two sites is also indicated by the pH dependence of activity.
