title: Subcellular localization of chorismate-mutase isoenzymes in protoplasts from mesophyll and suspension-cultured cells of Nicotiana silvestris.
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.
authors.affiliation: Center for Somatic-cell Genetics and Biochemistry, Department of Biological Sciences, State University of New York, 13901, Binghamton, NY, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: d'Amato
authors.forename: R J
authors.initials: RJ
authors.lastname: Ganson
authors.forename: C G
authors.initials: CG
authors.lastname: Gaines
authors.forename: R A
authors.initials: RA
authors.lastname: Jensen