Purification par chromatographie d'affinité d'une acétyltransférase et d'une phosphotransférase inactivant les antibiotiques aminosidiques

Antibiotic uptake by bacteria as measured by partition in polymer aqueous phase systems

Polyethyleneglycol/dextran and polyethyleneglycol/salt two-phase systems are used to measure the entry of antibiotics into Escherichia coli and Staphylococcus aureus cells. Aminoglycosides, macrolides, a quinolone, and a cycline were assayed. The method is simple and rapid and eliminates the problems encountered with filters, especially nonspecific binding; it allows rapid uptake kinetics to be measured.

A study of the enzymatic inactivation of chloramphenicol by highly purified chloramphenicol acetyltransferase

We report the purification of chloramphenicol acetyltransferase (acetyl-CoA:chloramphenicol 3-O-acetyltransferase, EC 2.3.1.28) by a two-step procecdure involving chromatography on a Sepharose 4B-reduced chloramphenicol matrix and DEAE-Sephadex A-50. This procedure resulted in a 120-fold purification with 50% recovery of the enzyme. Only one band of enzyme activity was present after electrophoresis on polyacrylamide gel. The enzyme is active over a broad pH range, maximal activity being observed near pH 7.6. Both chloramphenicol 1-acetate of chloramphenicol 3-acetate were found to be very stable in Tris-maleate buffer at pH 6.09 with negligible interconversion. The incubation at pH 6.0 of chloramphenicol 1-acetate with the purified chloramphenicol acetyltransferase yielded chloramphenicol 1,3-diacetate. These data indicate that the enzyme acetylates specifically at the 3-hydroxy position and the diacetylation is possible only because of non-enzymatic interconversion of chloramphenicol 3-acetate to chloramphenicol 1-acetate at higher pH values.

[Purification of the bacterial ribosome using chloramphenicol and erythromycin columns]

Chloramphenicol and erythromycin are antibiotics whose target is the bacterial ribosome. We have studied the possibility of isolating the bacterial ribosome by affinity chromatography on chloramphenicol and erythromycin columns. Several columns have been prepared using different spacers and methods of attachment of the ligands (cyanogen bromide, bis-expoxyde). The efficiency and specificity of these columns is discussed. Ethylene diamine is not always suitable as a spacer, because it presents non specific affinity for the ribosome. Pure tight ribosomes have been prepared by ultracentrifugation. They have been compared to ribosomes from affinity columns. These columns have no denaturing effect on ribosomes. They allow a good purification of ribosomes starting from crude bacterial extracts, but the separation of tight couples from loose subunits is not possible.

[Immobilization of coenzyme A on a hydrosoluble polymer]

Our purpose being to work out a "continuous flow" enzymatic reactor of acetylation with a cofactor, we present here some results about the immobilization of coenzyme A on T40 dextran. Two methods of fixation are compared with regard to the capacity and the biological activity of the polymers thus obtained.