UV‐ACTION SPECTRUM (254‐405 nm) FOR INHIBITION OF A K⁺ ‐STIMULATED ADENOSINE TRIPHOSPHATASE FROM THE PLASMA MEMBRANE OF ROSA DAMASCENA

A K + ‐stimulated ATPase from suspension‐cultured rose cells was isolated and subjected to UV radiation. The characteristics of the ATPase resembled those of a plasma‐membrane associated enzyme and not those of the mitochondrial enzyme. The ATPase required Mg 2+ and was further stimulated up to 100% by K + . K + stimulation was specific for ATP. The order of stimulation by monovalent cations was K + > Na + > Li + . The enzyme had a pH optimum of 6.5 in the presence of 50 mM K + . It was almost completely inhibited by diethylstilbestrol and partially inhibited by vanadate. but was not affected by azide or oligomycin. The inhibition of ATPase activity by various fluences of UV indicated that one fraction of the K + ‐stimulated activity was very sensitive to radiation, while another fraction was relatively insensitive. It is possible that UV distinguished between two enzymes. The action spectra for inhibition of both fractions showed maxima at 290 nm and significant but much lower action throughout the near‐UV region, resembling spectra in the literature for the inhibition of transport processes in bacteria.