EFFECT OF ISONIAZID ON THE INCORPORATION OF SOME RADIOACTIVE SUBSTANCES INTO THE CELLULAR FRACTIONS OF A STRAIN OF MYCOBACTERIUM

Resolution and identification of ribosomes from mycobacteria

Ribosomes were isolated from mycobacteria (BCG) by differential centrifugation by use of a modification of Nirenberg's procedure. Individual components of the ribosomal spectrum were resolved in linear sucrose density gradients. Sedimentation constants of the individual components were determined by analytical ultracentrifugation. Ribosomes from escherichia coli labeled with (14)C-uracil were used as markers for an independent confirmation of the identity of individual peaks. The typical ribosomal spectrum of 70S units and 50S and 30S subunits was obtained in tris(hydroxymethyl)aminomethane buffer with 0.01 m Mg(CH(3)COO)(2). This corresponds to the ribosomal spectrum obtained in E. coli under comparable conditions. In 0.0001 m Mg(2+), the 70S units were dissociated to 50S and 30S particles. Pancreatic ribonuclease produced no significant changes in main ribosomal components. The isolation techniques used in this work precluded the recognition of polyribosomes.

Effects of isoniazid on the composition of mycobacteria, with particular reference to soluble carbohydrates and related substances

1. When growing Mycobacterium tuberculosis BCG was exposed to 0.5-10mug. of isoniazid/ml. there was intracellular accumulation of soluble carbohydrate, combined phosphate and substances absorbing at 260mmu. Yellow pigments were formed when modified Sauton medium was used, but not with Proskauer & Beck medium. These processes were apparent after 1hr. but were more marked after about 6hr. These effects were not found with an isoniazid-resistant strain. 2. After 6hr. exposure of the sensitive strain to 10mug./ml. there was little change in the amounts (per g. of insoluble nitrogen) of total lipid, glycolipid, RNA, DNA or of carbohydrate in the nucleic acid fractions. 3. The major accumulation was of alphaalpha'-trehalose. There was also accumulation of glucose 6-phosphate, glucose 1-phosphate, fructose 6-phosphate, trehalose 6-phosphate (tentatively identified), a polysaccharide containing only glucose, and an oligosaccharide containing glucose and glucose 6-phosphate, but not of glycerol and glycerol 3-phosphate. The u.v.-absorbing materials appeared to be nucleotide sugar derivatives. 4. In Mycobacterium smegmatis a similar accumulation of trehalose occurred on exposure to isoniazid, but there was little accumulation of other compounds. 5. No evidence could be found that isoniazid specifically affected the oxidation of glycerol or glycerol 3-phosphate. 6. It is suggested that the primary action of isoniazid on mycobacteria may be partial inhibition of a reaction in some central area of metabolism, such as glycolysis.