Louise E. Anderson, PhD
845 West Taylor St.
Plant Enzymes and Plant Proteins; Photosynthetic Carbon Metabolism
Light Activation - An On/Off Switch
Several enzymes of photosynthetic CO2 fixation are light activated in the chloroplast. Other enzymes that are involved in the degradation of sugars are light inactivated. Light modulation involves the transfer of electrons from the photochemical apparatus through a series of carriers to thioredoxin, which reduces disulfides on the target enzymes. Why do these disulfides affect the activity of the target enzymes and which cysteine residues are involved? Are there enzymes outside of the chloroplast that are also redox-sensitive? We are collaborating with Jack Watson's lab at Michigan State in the identification of the redox-sensitive cysteine residues in the redox-sensitive plant enzymes, both chloroplastic and cytosolic, by mass mapping.
Enzyme-Enzyme Interaction in the Chloroplast
Are intermediates passed from one enzyme to the next in the chloroplast? We have developed a quantitative method to assess co-localization of immunolabeled proteins on electron micrographs. Results to date indicate that, with one exception, each of the enzymes of CO2 fixation is co-localized with the enzyme that generates its substrate and utilizes its product, consistent with the idea that intermediates are channeled between the enzymes of the Calvin cycle.
Unexpected Proteins in the Nucleus
Immunocytolocalization experiments indicate that both the chloroplastic and cytosolic forms of the carbon metabolism enzymes aldolase, glyceraldehyde-3-P dehydrogenase, P-glycerate kinase and fructose bisphosphatase are present in the pea leaf nucleus, where it seems unlikely that they are involved in glycolysis or gluconeogenesis. There are profound differences in levels of some of these enzymes in the nuclei in the leaf at the base of the plant and in the apical leaf, suggesting that these proteins might have a role in gene expression related to senescence or leaf development. These enzymes are co-localized with DNA in the nucleus. Whether they bind DNA and whether there is specificity in that binding remains to be determined.
Anderson LE and Carol AA (2004) Enzyme Co-Localization with Rubisco in Pea Leaf Chloroplasts. Photosyn. Res., 82:49-58.
Anderson LE, Ringenberg MR, Carol AA (2004) Cytosolic Glyceraldehyde-3-P Dehydrogenase and the B Subunit of the Chloroplast Enzyme are present in the Pea Leaf Nucleus. Protoplasma 223:33-43
Anderson JB, Carol AA, Brown VK, and Anderson LE (2003) A Quantitative Method for Assessing Co-localization in Immuno-labeled Thin Section Electron Micrographs. J. Structural Biol., 143:95-106.
Qi J, Isupov MN, Littlechild JA and Anderson LE (2001) Chloroplast Glyceraldehyde-3-P Dehydrogenase Contains a Single Disulfide Bond Located in the C-Terminal Extension to the B Subunit. J Biol Chem 276:35247-35252.
Anderson LE, Li AD, Muslin EH, Schiffer M and Stevens FJ (2000) Identifying Redox-Sensitive Extra-Chloroplastic Enzymes by Homology Modeling. Physiol Plant 110:296-302.