Changes in activity and isoenzymes of invertase in cucumber leaves due to nitrogen status

When 20 ppm ammonium nitrogen was supplied to nitrogen starvedcucumbers, acid and alkaline invertase activities increased6 and 2 fold on a fresh weight basis, respectively. Two acidinvertase isozymes, I and II, were detected in cucumber leavesby DEAE cellulose chromatography and Sephadex G-100 gel filtration.Their activities were found to be reversed in nitrogen-starvedand -sufficient cucumber leaves, isozyme II being the majorisozyme in nitrogen sufficient plant. Isozyme II had nearlyhalf the Km value of I for sucrose, and hydrolyzed raffinoseless than half as much as I did, although they showed the nearlysame pH optimum at 5.0 and similar heat stability. These resultsare discussed in relation to the regulatory role of acid invertasein cucumber leaves under different nitrogen status. (Received March 26, 1976; )