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Letter from Joshua Lederberg to Hugo Theorell

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  • Biology
  • Chemistry
  • Medicine

Abstract

-’ / THE BETA-D-GALACTOSIDASE OF ESCHERICHIA COLI, STRAIN K-12 JOSHUA LEDERBERG Department of Genetics, College of Agricdture, University of Wisconsin, Madison, Wisconsin Reprinted from Joumar. OF Bncraxuo~oor Vol. t&J, No. 4. October, 1959 Made in United States of America Reprinted from JOURNAL OF BACTERIOLOGY Vol. 60, No. 4, October, 1950 THE BETA-D-GALACTOSIDASE OF ESCHERICHIA COLI, STRAIN K-12l JOSHUA LEDERBERG Department of Genetics, College of Agriculture, University of Wisconsin, Madison, Wisconsin* Received for publication June 26, 1950 The glycolysis of lactose by Escherichia coli is of interest for the biochemical problem of disaccharide utilization and as a point of at,tack for studies of the genetic basis of enzyme constitution. As a basis for further studies in these direc- tions, the present study has been made of a 8-D-galactoside-splitting enzyme in cells of strain K-12. This strain was chosen because of its suitability for genetic analysis by recombination methods (Lederberg, 1947). METHODS Cell-free extracts. Most preparations were made from cells grown in aerated liquid medium, either a synthetic medium with lactose as the sole carbon source or a complete medium containing 0.1 to 1.0 per cent lactose as well as peptone or tryptic digest of casein. Some preparations were made from cells grown on agar plates. No differences in behavior were apparent between various prepara- tions. The cells were washed with sterile water, by centrifugation and resuspen- sion. Extracts were most conveniently prepared from cells dried in vacua over PZOS at room temperature. Autolysis under benzene and crushing with powdered glass were also successful. Dried cells were triturated and shaken for 2 to 3 hours at 37 C with 50 to 100 volumes of water or buffer. Debris was sedimented at 3,500 rpm for 15 minutes and discarded. The supernatant was usually opalescent but free of bacterial cells or large fragments. Most of the experimen

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