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. 1984 Feb;74(2):374–379. doi: 10.1104/pp.74.2.374

Spinach Pyruvate Kinase Isoforms 1

Partial Purification and Regulatory Properties

Chris Baysdorfer 1,2, James A Bassham 1,2
PMCID: PMC1066685  PMID: 16663425

Abstract

Pyruvate kinase from spinach (Spinacea oleracea L.) leaves consists of two isoforms, separable by blue agarose chromatography. Both isoforms share similar pH profiles and substrate and alternate nucleotide Km values. In addition, both isoforms are inhibited by oxalate and ATP and activated by AMP. The isoforms differ in their response to three key metabolites; citrate, aspartate, and glutamate. The first isoform is similar to previously reported plant pyruvate kinases in its sensitivity to citrate inhibition. The Ki for this inhibition is 1.2 millimolar citrate. The second isoform is not affected by citrate but is regulated by aspartate and glutamate. Aspartate is an activator with a Ka of 0.05 millimolar, and glutamate is an inhibitor with a Ki of 0.68 millimolar. A pyruvate kinase with these properties has not been previously reported. Based on these considerations, we suggest that the activity of the first isoform is regulated by respiratory metabolism. The second isoform, in contrast, may be regulated by the demand for carbon skeletons for use in ammonia assimilation.

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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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