Résumé
Adenosine phosphorylase, a purine nucleoside phosphorylase endowed with high specificity for adenine nucleosides, was purified 117-fold from vegetative forms of
Bacillus cereus. The purification procedure included ammonium sulphate fractionation, pH 4 treatment, ion exchange chromatography on DEAE-Sephacel, gel filtration on Sephacryl S-300 HR and affinity chromatography on N
6-adenosyl agarose. The enzyme shows a good stability to both temperature and pH. It appears to be a homohexamer of 164
±
5 kDa. Kinetic characterization confirmed the specificity of this phosphorylase for 6-aminopurine nucleosides. Adenosine was the preferred substrate for nucleoside phosphorolysis (
k
cat/
K
m 2.1
×
10
6 s
−
1
M
−
1
), followed by 2′-deoxyadenosine (
k
cat/
K
m 4.2
×
10
5 s
−
1
M
−
1
). Apparently, the low specificity of adenosine phosphorylase towards 6-oxopurine nucleosides is due to a slow catalytic rate rather than to poor substrate binding.