Subcellular localization of chorismate-mutase isoenzymes in protoplasts from mesophyll and suspension-cultured cells of Nicotiana silvestris |
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Authors: | d'Amato T. A. Ganson R. J. Gaines C. G. Jensen R. A. |
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Affiliation: | (1) Center for Somatic-cell Genetics and Biochemistry, Department of Biological Sciences, State University of New York, 13901 Binghamton, NY, USA |
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Abstract: | The subcellular locations of two readily discriminated chorismate-mutase (EC 5.4.99.5) isoenzymes from Nicotiana silvestris Speg. et Comes were determined in protoplasts prepared from both leaf tissue and isogenic suspension-cultured cells. Differential centrifugation was used to obtain fractions containing plastids, a mixture of mitochondria and microbodies, and soluble cytosolic proteins. Isoenzyme CM-1 is sensitive to feedback inhibition by l-tyrosine and comprises the major fraction of total chorismate mutase in suspension-cultured cells. Isoenzyme CM-2 is not inhibited by l-tyrosine and its expression is maximal in organismal (leaf) tissue. Isoenzyme CM-1 is located in the plastid compartment since (i) proplastids contained more CM-1 activity than chloroplasts, (ii) both chloroplast and proplastid fractions possessed the tyrosine-sensitive isoenzyme, and (iii) latency determinations on washed chloroplast preparations confirmed the internal location of a tyrosine-sensitive isoenzyme. Isoenzyme CM-2 is located in the cytosol since (i) the supernatant fractions were heavily enriched for the tyrosineinsensitive activity, and (ii) a relatively greater amount of tyrosine-insensitive enzyme was present in the supernatant fraction derived from organismal tissue. |
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Keywords: | Chorismate mutase Isoenzyme Nicotiana (chorismate mutase) |
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