Comparison of nitrophenylethyl and hydroxyphenacyl caging groups

Nitrophenylethyl (NPE)- and hydroxyphenacyl (HPA)-caged nucleotides were em ployed in a time-resolved Fourier transform IR spectroscopy study on Ras-ca talyzed guanosine triphosphate (GTP) hydrolysis. A fast kinetic component w as observed following the photolysis of NPE-caged nucleotides in the NPE-GT P-Ras complex. However, this kinetic component was not observed in the HPA- GTP-Ras experiment. This fast kinetic component was likely due to a chemica l reaction between Ras and the detached caging group, nitrosoacetophenone. This communication serves as a note of caution in interpreting spectral cha nges and kinetic behavior of the enzymatic systems employing NPE-caged comp ounds. (C) 2001 John Wiley & Sons, Inc.