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Enzymes Catalyzing Anaplerotic Carbon Dioxide Fixation in Verticillium albo-atrum. R. E. Hartman, Professor of Biology, St. Bonaventure University, St. Bonaventure, New York 14778; N. T. Keen, Associate Professor of Plant Pathology, University of California, Riverside 92502. Phytopathology 63:947-953. Accepted for publication 2 February 1973. DOI: 10.1094/Phyto-63-947.

Pyruvate carboxylase and phosphoenolpyruvate carboxykinase activities were present in extracts from Verticillium albo-atrum. Nondialyzed extracts actively fixed NaH14CO3 when supplied either pyruvate and ATP or phosphoenolpyruvate (PEP) and ADP. Pyruvate plus NADH or NADPH did not produce CO2 fixation; PEP alone or with phosphate also was ineffective. The carbon-14 was incorporated into aspartate and citrate by the crude extracts. Enzyme extracts dialyzed against pH 6.6 phosphate buffer utilized only pyruvate and ATP (pyruvate carboxylase activity); whereas, extracts dialyzed against pH 7.6 tris buffer required PEP and ADP for fixation of 14CO2 (PEP carboxykinase). Oxalacetate was considered as the primary fixation product in both cases. Incubation of the crude extracts with oxalacetate for 30 min prior to dialysis enhanced pyruvate carboxylase activity. Both enzymes appeared to occur primarily in the cytosol although a significant level of PEP carboxykinase also was associated with the mitochondrial fraction.

Additional keywords: pyruvate carboxylase, phosphoenolpyruvate carboxykinase.