Nucleoside diphosphatase in the onion root tip. I. Effects of fixation and lead on enzyme activity.

Abstract

The terminal 0.2—0.5 mm of 3-day onion roots grown from bulbs were excised and fixed for 1½ hr in various concentrations of cacodylate-buffered glutaraldehyde, formaldehyde or combinations of these. Alternatively, the fixative concentration was held constant while fixation time was varied. Control roots were run in buffer lacking fixative. The roots were then homogenized and in most cases aliquots of the entire homogenate were used to assay for total nucleoside diphosphatase (NDPase). Parallel assays were usually run after treating the homogenate with deoxycholate. Both glutaraldehyde and formaldehyde inhibited NDPase activity, the extent of this inhibition depending upon fixation time, fixative concentration and the particular aldehyde used, although with both fixatives inhibition did not increase beyond a certain level even with further increase in fixation time or fixative concentration. With glutaraldehyde and glutaraldehyde-containing fixatives, this level was normally about 74% inhibition while with formaldehyde it was about the level of non-activated NDPase activity and inhibition could be detected only after deoxycholate treatment. Lead did not appear to inhibit the "fixed" NDPase.