title: Mechanism of action of sparsomycin in protein synthesis.
abstract: Before CI isomerizes to C*I, we detect a competitive phase of inhibition (Ki = k5/k4 = 0.05 microM) which eventually, by increasing the concentration of I, becomes linear mixed noncompetitive and involves C*I in place of CI. The equilibration of C and I according to reaction 2 is much slower than the equilibration between C and S in reaction 1 (time-dependent inhibition). The inactivation plots obey reaction 2 and allow us to estimate k6 as equal to 2.2 min-1. The isomerized C*I, free of excess I, can be studied as a mixture with complex C. From the kinetics of the regeneration of C from C*I, in the presence of puromycin, we can estimate k7 to be between 0.22 min-1 and 0.06 min-1. Although the isomerized C*I survives after adsorption on cellulose nitrate filter disks, it does not survive after gel chromatography on a Sepharose CL-4B column but is converted quantitatively to complex C containing D of unchanged reactivity. This result does not support the proposed [Flynn, G. A., & Ash, R. J., (1990) Biochem. Biophys. Res. Commun. 166, 673-680] chemical reaction between D and I toward new products. The isomerized C*I can be obtained not only from the already-made complex C but also de novo from D, R, and M. In the latter case, the reactions which lead to C are represented by the following hypothetical scheme: D + R + M in equilibrium with DRM or C (binding reaction). When C*I is formed de novo, this reaction is coupled to reaction 2 and the ultimate product is a mixture of C and C*I.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Laboratory of Biochemistry, School of Medicine, University of Patras, Greece.
authors.forename: D A
authors.initials: DA
authors.lastname: Theocharis
authors.forename: C
authors.initials: C
authors.lastname: Coutsogeorgopoulos
mesh_terms: D001667:Binding, Competitive; D002850:Chromatography, Gel; D004926:Escherichia coli / Q000378:metabolism; D007700:Kinetics; D014176:Protein Biosynthesis; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology*; D011691:Puromycin / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D013033:Sparsomycin / Q000494:pharmacology*
chemical_list: D011500:Protein Synthesis Inhibitors; D012346:RNA, Transfer, Amino Acyl; C006383:tRNA, N-acetylphenylalanine-; D011691:Puromycin; D013033:Sparsomycin