It is possible to determine the anomeric configuration of nucleosides by a simple, spectrophotometric assay, using the nucleoside phosphorylase activity of cell-free extracts from E. coli. β-nucleo-sides are split, a-anomers remain unchanged. For a single estimation 20-40 µg of nucleoside are required. 6-Azauracil- and 8-azaguanine-β-ᴅ-riboside and some nucleoside phosphates are resistant, a fact, which is of interest in view of the specificity of nucleoside phosphorylases.
Steroid initiated enzyme induction (Δ5-Ketosteroid-Isomerase, 3α-Hydroxysteroid-Dehydrogenase, and 3β.17β-Hydroxysteroid-Dehydrogenase) in Pseudomonas testosteroni was investigated with respect to the kinetics of induction, operon control of the induced enzymes, and the relative strengths of various inducers. The induction process was followed indirectly by selective inhibition of different stages in the protein synthetic pathway. Comparisons between bacterial and mammalian steroid induction are discussed.
Induction of the enzyme Δ5-3-ketosteroid isomerase in Pseudomonas testosteroni was found to be strongly inhibited by reserpine and by the alkaloids of Vinca and Ergot. Morphine, colchicine and papaverine caused weaker inhibition whilst a series of other alkaloids were almost ineffective. Ergot alkaloids were inhibitory towards all steroids tested, androgens, oestrogens and progestagens, and a similar effect was shown with the other inducible enzymes, 3α- and 3β.17β-hydroxysteroid-dehydrogenase.
Experiments with cell-free protein synthesis indicate that reserpine inhibits the induction of messenger RNA.
At pH 5.3 and 4.5 the half life of valyl-, threonyl-, leucyl- and seryl-tRNA from E. coli K 12 is significantly higher than at pH 6.8. While no changes were observed in the MAK elution patterns of valyl- and threonyl-tRNA, leucyl-tRNA was eluted in two peaks at pH 6.8 and 5.3 and in one broad peak at pH 4.5. Seryl-TRNA - two peaks at pH 6.8 - was separated in three peaks at pH 5.3 and 4.5. Rechromatography of these peaks at the other pH suggests the existence of at least four species of seryl-tRNA in E. coli K 12.