STUDIES ON THE PLANT METHYLCROTONYL-COA CARBOXYLASE

In our research on the presence of biotin-containing carboxylases in p lants we found, in addition to acetyl-CoA carboxylase (ACC), the carbo xylation of propionyl-CoA (PCC-activity) and methylcrotonyl-CoA (MCC-a ctivity) in protein preparations from maize, oat, barley, pea and lent il. Whether the PCC-activity originates from a distinct, separate enzy me or represents a side-activity of the ACC is not yet clear. The carb oxylation of methylcrotonyl-CoA is clearly catalyzed by a new biotin e nzyme, the methylcrotonyl-CoA carboxylase (MCC), which can be inhibite d by avidin. It is not present in isolated chloroplasts, but seems to be a component of plant mitochondria. In contrast to ACC and PCC, the MCC of barley and maize is not inhibited by two herbicide groups, know n to be strong inhibitors of the ACC from grasses. The activity of ACC and MCC from maize exhibit a quite different developmental pattern: A CC is found in young leaf tissue, whereas MCC shows up only in older t issue. The MCC from barley was purified 60-fold using different HPLC c olumns.