title: Sparsomycin and its analogues: a new approach for evaluating their potency as inhibitors of peptide bond formation.
abstract: The ability of several sparsomycin analogues to inhibit peptide bond formation was studied in vitro. Peptide bonds are formed between puromycin (S) and the acetylPhe-tRNA of acetylPhe-tRNA/70 S ribosome/poly(U) complex (complex C), according to the puromycin reaction: [formula: see text] It was shown that the sparsomycin analogues, like sparsomycin itself, inhibit peptide bond formation in a time-dependent manner; they react with complex C according to the equation [formula: see text] where C*I is a conformationally altered species in which I is bound more tightly than in CI. The determination of the rate constant k(7) for the regeneration of complex C from the C*I complex allows evaluation of these analogues as inhibitors of peptide bond formation. According to their k7 values, these analogues are classified in order of descending potency as follows: n-pentyl-sparsomycin (4) > n-butyl-sparsomycin (3) approximately n-butyl-deshydroxy-sparsomycin (6) > benzyl-sparsomycin (2) > deshydroxy-sparsomycin (5) approximately sparsomycin (1) > n-propyl-desthio-deshydroxy-sparsomycin (7). The analogues with an aromatic or a larger hydrophobic side chain are stronger inhibitors of the puromycin reaction than are those with a smaller side chain or those lacking the bivalent sulfur atoms; replacement of the hydroxymethyl group with a methyl group does not affect the position of the compound in this ranking; compare the positions of compounds 1 and 3 with those of 5 and 6. In the case of compound 7, C*I adsorbed on cellulose nitrate disks was not sufficiently stable to allow examination by the method applied to the other analogues, probably due to a relatively large value of k7. This analogue showed also time-dependent inhibition, but after the isomerization of CI to C*I, the kinetics of inhibition become complex, and C*I interacted further with puromycin, either as C*I or after its dissociation to C*.
authors.affiliation: Laboratory of Biochemistry, School of Medicine, University of Patras, Greece.
authors.forename: S
authors.initials: S
authors.lastname: Kallia-Raftopoulos
authors.forename: D
authors.initials: D
authors.lastname: Synetos
authors.forename: H C
authors.initials: HC
authors.lastname: Ottenheijm
authors.forename: L A
authors.initials: LA
authors.lastname: van den Broek
authors.forename: C
authors.initials: C
authors.lastname: Coutsogeorgopoulos
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D007700:Kinetics; D010458:Peptidyl Transferases / Q000037:antagonists & inhibitors*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology*; D013033:Sparsomycin / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D000903:Antibiotics, Antineoplastic; D011500:Protein Synthesis Inhibitors; D013033:Sparsomycin; D010458:Peptidyl Transferases