title: Carbon isotope fractionation by ribulose-1,5-bisophosphate carboxylase from various organisms.
abstract: Carbon isotope fractionation by structurally and catalytically distinct ribulose-1,5-bisphosphate carboxylases from one eucaryotic and four procaryotic organisms has been measured under nitrogen. The average fractionation for 40 experiments was -34.1 per thousand with respect to the delta(13)C of the dissolved CO(2) used, although average fractionations for each enzyme varied slightly: spinach carboxylase, -36.5 per thousand; Hydrogenomonas eutropha, -38.7 per thousand; Agmenellum quadruplicatum, -32.2 per thousand; Rhodospirillum rubrum, -32.1 per thousand; Rhodopseudomonas sphaeroides peak I carboxylase, -31.4 per thousand; and R. sphaeroides peak II carboxylase, -28.3 per thousand. The carbon isotope fractionation value was largely independent of method of enzyme preparation, purity, or reaction temperature, but in the case of spinach ribulose-1,5-bisphosphate carboxylase fractionation, changing the metal cofactor used for enzyme activation had a distinct effect on the fractionation value. The fractionation value of -36.5 per thousand with Mg(2+) as activator shifted to -29.9 per thousand with Ni(2+) as activator and to -41.7 per thousand with Mn(2+) as activator. These dramatic metal effects on carbon isotope fractionation may be useful in examining the catalytic site of the enzyme.
authors: University of Texas, Marine Science Institute, Port Aransas Marine Laboratory, Port Aransas, Texas 78373.
authors: M F
authors: MF
authors: Estep
authors: F R
authors: FR
authors: Tabita
authors: P L
authors: PL
authors: Parker
authors: C
authors: C
authors: Van Baalen