Actinomycins kinetics

The preceding studies with radioisotopes have provided information concerning the amino acids which serve as precursors for the biogenesis of the actinomycins. Kinetic studies (Fig. 4) of the rate of incorporation of C-labeled amino acids into the antibiotic during short incubations (30 to 120 minute intervals) have also provided considerable information concerning actinomycin s mthesis (Katz and Weissbach 1962, 1963). This has been possible because actinomycin is readily soluble in organic solvents, e.g., ethyl acetate, whereas the amino acid precursors are not. Once the antibiotic is extracted into ethyl acetate, the radioactivity incorporated into the antibiotic as a function of time can be determined by conventional techniques of liquid scintillation counting. 

Actinomycin D dissociation kinetics were measured on a Cary 219 spectrophotometer equipped with a magnetic stirrer and thermostated cell holders. Sodium dodecyl sulfate (SDS) was used to sequester dissociating actinomycin D, and the resulting Increase In absorbance was monitored at 452 nm as a function of time. Stop-flow studies (daunorubicin and daunorubicin/ actinomycin D) were conducted with a Durrum-Glbson Model 110 stopped-flow spectrophotometer equipped with a dual detector accessory and a Tektronix storage oscilloscope Interfaced with a PDF 11/34 computer. Experiments were done In a 0.01M Na phosphate buffer, 0.1M NaCl, 0.001M NaEDTA, pH=7. Dissociation time constants were computed with a multlexponentlal analysis computer program. 

Kinetics. The dissociation of actinomycin D from poly(dGdC)-poly(dGdC) Is well described by a single exponential decay (Table... 

The dissociation kinetics of daunorubicin and daunorubicin actinomycin D from poly(dAdT).poly(dAdT) were studied using stopped-flow techniques. The data is summarized in Table IV. The dissociation of daunorubicin from poly(dAdT).poly(dAdT) is monophaslc with a lifetime of 0.2 sec. In the ternary complex (daunorubicin actinomycin D poly(dAdT).poly(dAdT)) the dissociation of the daunorubicin is characterized by two exponential decays, yielding lifetimes of 0.2 sec and 5 sec, A single 5 sec dissociation time was observed for actinomycin D. 

Actlnomvcin D - Kinetic studies with actinomycin D (act-D) in transplanted leukemic mice showed that a single dose provided cytotoxic concentrations for up to 24 hours,The characteristics of act-D resistance in L5178Y cells show that alterations in membrane composition and conformation in the drug-resistant subline accounts for the observed changes in the permeability of this drug.91 Act-D enhances the toxicity of morphine by increasing brain permeability. ... 

Fig. 13a and b. Kinetics of incorporation of L-threonine- and L-proline- C into the amino acid pool, protein and actinomycin by S. antihioticus in the presence and absence of chloramphenicol. 13a 5. antihioticus was grown for 48 hours in glutamic acid medium at which time the actinomycin titer was 16 (xg/ml. L-threonine- C (9.5 X 10 cpm/ml, 4X10 M) and chloramphenicol (30 xg/ml) were supplied simultaneously to one culture. Protein was 0.35 mg and mycelium, 1.72mg (dry weight) per ml. 

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