Open AccessThermodynamics and kinetics of the cleavage of DNA catalyzed by bleomycin A 5
Author(s) -
Liang Yi,
Du Fen,
Zhou BingRui,
Zhou Hui,
Zou GuoLin,
Wang CunXin,
Qu SongSheng
Publication year - 2002
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1033.2002.02948.x
Subject(s) - chemistry , dna , kinetics , enthalpy , cleavage (geology) , bond cleavage , catalysis , endonuclease , michaelis–menten kinetics , stereochemistry , enzyme , biochemistry , biology , enzyme assay , thermodynamics , paleontology , physics , quantum mechanics , fracture (geology)
Microcalorimetry and UV‐vis spectroscopy were used to conduct thermodynamic and kinetic investigations of the scission of calf thymus DNA catalyzed by bleomycin A 5 (BLM‐A 5 ) in the presence of ferrous ion and oxygen. The molar reaction enthalpy for the cleavage, the Michaelis–Menten constant for calf thymus DNA and the turnover number of BLM‐A 5 were calculated by a novel thermokinetic method for an enzyme‐catalyzed reaction to be −577 ± 19 kJ·mol −1 , 20.4 ± 3.8 µ m and 2.28 ± 0.49 × 10 −2 s −1 , respectively, at 37.0 °C. This DNA cleavage was a largely exothermic reaction. The catalytic efficiency of BLM‐A 5 is of the same order of magnitude as that of lysozyme but several orders of magnitude lower than those of Taq I restriction endonuclease, Nae I endonuclease and Bam HI endonuclease. By comparing the molar enthalpy change for the cleavage of calf thymus DNA induced by BLM‐A 5 with those for the scission of calf thymus DNA mediated by adriamycin and by (1,10‐phenanthroline)‐copper, it was found that BLM‐A 5 possessed the highest DNA cleavage efficiency among these DNA‐damaging agents. These results suggest that BLM‐A 5 is not as efficient as a DNA‐cleaving enzyme although the cleavage of DNA by BLM‐A 5 follows Michaelis–Menten kinetics. Binding of BLM‐A 5 to calf thymus DNA is driven by a favorable entropy increase with a less favorable enthalpy decrease, in line with a partial intercalation mode involved in BLM‐catalyzed breakage of DNA.