Photoactivated heterobifunctional cross-linking reagents which demonstrate the aggregation state of phospholipase A2

Two novel heterobifunctional cross-linking reagents, which can be used to attach photoactivatable nitroaryl azides to primary amino groups of proteins, have been synthesized. The two compounds, N-5-azido-2-nitrobenzoyloxy-succinimide and ethyl N-5-azido-2-nitrobenzoylaminoacet-imidate-HCl, as well as ethyl 4-azidobenzimidate-HCl have been attached to lysine residues of cobra venom phospholipase A2 without a loss in enzymatic activity. Subsequent illumination of the modified forms of the enzyme at appropriate wavelengths under conditions in which the native enzyme exists in an aggregated state led to the formation of covalently linked dimers and large aggregates which could be separated by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate.     

A study of the electron emission characteristics of a triggered vacuum switch

Details are given of the construction and operational characteristics of a triggered vacuum switch suitable for operation over a wide range of voltage. To gain an insight into the physical basis of the performance of the device, two in situ analytical techniques have been employed to study the electron emission characteristics. Firstly, an anode probe hole technique, incorporating a new automated two-dimensional electrode scanning facility, has been used to display the spatial distribution of the electron emission associated with the ‘firing’ mode of the triggered vacuum switch. Secondly, the energy spectrum of this emission has been recorded using a high resolution electron spectrometer that is interfaced with the above facility. In conclusion, a qualitative discussion aims to interpret the physical significance of the experimental findings.