triostin-c and quinomycin

Protoplasts of Streptomyces echinatus have been used to investigate the biosynthesis of echinomycin (quinomycin A). It has been shown that this organism has the capacity to convert a series of triostins to the corresponding quinomycins by a mechanism involving methylation. Evidence is presented which suggests that triostin A is the natural precursor of echinomycin. Conversion of tetra-N-demethyl analogues of triostin A to corresponding analogues of echinomycin was not detected.

Topics: Anti-Bacterial Agents; Carbon Radioisotopes; Echinomycin; Kinetics; Protoplasts; Quinoxalines; Streptomyces; Sulfur Radioisotopes

The kinetics of detergent-induced dissociation of triostins A and C and quinomycin C from DNA have been investigated. All three antibiotics dissociate from poly(dA-dT) and poly(dG-dC) in a simple first-order fashion whereas their dissociation from a natural DNA (calf thymus) is complex, requiring three exponential terms for its complete description. This behaviour is attributed to sequence-selectivity on the part of the drugs and seems to represent dissociation from different classes of intercalative binding site. The time constants of dissociation are better resolved for quinomycins than for triostins, consistent with the view that quinomycins are more sequence-specific in their interaction with DNA, but it is not possible to identify any class of binding site with the alternating purine-pyrimidine sequences of the synthetic polydeoxynucleotides. In general, the triostins dissociate an order of magnitude faster than the corresponding quinomycins. This is attributable to a larger entropy of activation, presumably reflecting greater flexibility of the octapeptide ring when the cross-bridge is a disulphide as opposed to the slightly shorter thioacetal found in quinomycins. The longest time constant in the dissociation of each of the four quinoxaline antibiotics from calf thymus DNA correlates well with its antibacterial potency, in agreement with the conclusion that the biological effects result from impairment of the role of DNA as a template for polymerase activity.

Topics: Animals; Anti-Bacterial Agents; Binding Sites; Cattle; DNA; Echinomycin; In Vitro Techniques; Kinetics; Quinoxalines; Structure-Activity Relationship; Thermodynamics