Organization of Polyaromatic Biosynthetic Enzymes in a Variety of Photosynthetic Organisms

Sucrose density gradient centrifugation was used to estimate the molecular weights and determine possible physical aggregation of the enzymes catalyzing steps 2 to 6 in pre-chorismic acid polyaromatic biosynthesis in Anabaena variabilis, Chlamydomonas reinhardi, Euglena gracilis, Nicotiana tabacum, and Physcomitrella patens. In A. variabilis, the five enzymes are separable. Similar results were obtained for P. patens, N. tabacum, and C. reinhardi extracts, except that dehydroshikimate reductase and dehydroquinase were not separable by this method. Evidence is presented for an enzyme aggregate containing five activities, with a molecular weight of approximately 120,000 in E. gracilis; dissociation of this aggregate into components corresponding to molecular weight of ca. 60,000 is also observed. Preliminary evidence concerning the enzymatic composition of the 60,000-molecular-weight components is presented and discussed. Similarities between the E. gracilis polyaromatic aggregate and that of Neurospora crassa are discussed.