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. 1981 Feb;67(2):330–334. doi: 10.1104/pp.67.2.330

Comparative Characterization of Phosphoenolpyruvate Carboxylase in C3, C4, and C3-C4 Intermediate Panicum Species 1

A Scott Holaday 1, Clanton C Black 1
PMCID: PMC425677  PMID: 16661669

Abstract

Various properties of phosphoenolpyruvate carboxylases were compared in leaf preparations from C3-C4 intermediate, C3, and C4Panicum species. Values of Vmax in micromoles per milligram chlorophyll per hour at pH 8.3 were 57 to 75 for the enzyme from Panicum milioides, Panicum schenckii, and Panicum decipiens (all C3-C4). The values for Panicum laxum (C3) and Panicum prionitis (C4) were 20 to 40 and 952 to 1374, respectively. The Vmax values did not change at pH 7.3 except for the C4 value, which increased about 24%. At pH 8.3, the phosphoenolpyruvate carboxylases from C3 and C3-C4 species had slightly higher Km HCO3− and lower K′ phosphoenolpyruvate values than did the C4 enzyme. With each species at pH 7.3, all K′ phosphoenolpyruvate values were 2- to 4-fold greater.

The enzyme from all species was inhibited 85 to 90% by 1 millimolar malate at rate-limiting phosphoenolpyruvate and Mg2+ levels. With low levels of malate, 0.2 millimolar, the rate curve with respect to phosphoenolpyruvate was distinctly sigmoidal, and the inhibition was not eliminated at 5 millimolar phosphoenolpyruvate.

Malate at 10 millimolar protected all phosphoenolpyruvate carboxylases from inactivation at 55 C at pH 5.5, but not at pH 8.3. Aspartate did not protect well. When incubated at 37 C at pH 8.3 without phosphoenolpyruvate, but with HCO3−, the enzyme from several C4 grasses lost 92 to 98% of the initial activity after 4 minutes, whereas the enzymes from C3 and C3-C4Panicum species retained 60 to 70% of their activities. In contrast, 5 millimolar phosphoenolpyruvate stabilized the enzyme at 37 C in all plant extracts.

The phosphoenolpyruvate carboxylase from C3-C4 intermediate Panicum species has properties most similar to the enzyme from C3Panicum species. The higher leaf activity of the enzyme from the intermediate plants than from C3 species is not due to any unusual property assayed other than a higher Vmax.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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