Abstract
An electrophoretic study was performed to determine the number of isoenzymes of nucleoside diphosphatase in onion root extract. Five bands exhibiting nucleoside diphosphatase activity were detected when gels were incubated with inosine diphosphate, uridine diphosphate, guanosine diphosphate or cytidine diphosphate as substrates. These consisted of a single fast migrating band (band one), a group of three intermediate migrating bands (bands two, three and four) and a single slow migrating band (band five). Gels incubated with adenosine diphosphate, thiamine pyrophosphate, inosine monophosphate, guanosine monophosphate and cytidine monophosphate showed only two bands (bands one and five). Inhibitor studies showed that sodium fluoride inhibited bands one and five but not bands two, three and four. Conversely, 1% (v/v) glutaraldehyde inhibited bands two, three and four but did not inhibit bands one and five. These results suggest that two separate groups of onion nucleoside diphosphatase isoenzymes occur which have different substrate specificities and are selected against by certain inhibitors.