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TRIBBY, ILSE I. E. (University of Chicago, Chicago, 111.), AND JAMES W. MOULDER. Availability of bases and nucleosides as precursors of nucleic acids in L cells and in the agent of meningopneumonitis. J. Bacteriol. 91:2362-2367. 1966.-Uninfected L cells and the meningopneumonitis agent propagated in L cells utilized exogenous adenine, guanine, and their ribonucleosides and deoxyribonucleosides for synthesis of both deoxyribonucleic acid (DNA) and ribonucleic acid. Cytosine, cytidine, and uridine were also incorporated into the nucleic acids of both host and parasite. L cells and the meningopneu.monitis agent incorporated uracil, thymine, and deoxyuridine very poorly. L cells utilized thymidine and deoxycytidine almost exclusively for DNA synthesis, but the meningopneu.monitis agent did not incorporate these nucleosides at all. Since the L cell had previously been shown to convert added thymidine to its nucleotides, mainly the triphosphate, it was concluded that the meningopneu.monitis agent can utilize neither the thymidine nor the thymidine nucleotides of the L-cell pool, and that it can probably synthesize the thymidine triphosphate needed for DNA synthesis from the uridine of the L-cell pool.

No abstract

Biochemical events accompanying changes in structure and behavior of the cell walls of Chlamydia psittaci strain 6BC during its developmental cycle in L cells

thranilic oxidase in these livers, it may be concluded that the failure of diabetic animals to synthesize nicotinic acid is not caused by a decrease in any essential enzyme, but must be attributed to some other type of control mechanism. The striking increase in picolinic carboxylase, from immeasurably low concentration to appreciable concentration, has previously been correlated with the decreased production of nicotinic acid. The decrease in quinolinic acid formation caused by an increase in picolinic carboxylase activity provides an adequate explanation for the control of nicotinic acid biosynthesis.The physiological significance of this phenomenon remains obscure, since it is not clear what advantage is gained by the diabetic organism through diverting an intermediate from nicotinic acid synthesis. The mechanism by which hormonal regulation of picolinic carboxylase operates is also not known. It does seem clear, however, that the more general phenomenon of competition for available substrate by different enzymes is exhibited in an extreme form in this system, in which the substrate for a spontaneous reaction is utilized by an enzyme whose activity changes from very low to higher values. 0.05 ml contained 0.5 mc of C14. 8. I. M. Gverdsiteli and S. G. Mikadze, J.Gen. Chem. 22, 1401 (1952); Chem. Abstr. 47, 6338 (1953). 9. Other characteristic peaks (not shown by maleic anhydride) 9.2 and 10.1 p,. Maleic anhydride gave strong maxima at 9.5 and 11.2 /1, not shown by the tetrahydrophthalic anhydride. In the preliminary pilot experiments a quick, roughly quantitative estimate of the percentage composition of the maleic anhydride-tetrahydrophthalic anhydride mixture (and therefore the percentage yield of thranilic oxidase in these livers, it may be concluded that the failure of diabetic animals to synthesize nicotinic acid is not caused by a decrease in any essential enzyme, but must be attributed to some other type of control mechanism. The striking increase in picolinic carboxylase, from immeasurably low concentration to appreciable concentration, has previously been correlated with the decreased production of nicotinic acid. The decrease in quinolinic acid formation caused by an increase in picolinic carboxylase activity provides an adequate explanation for the control of nicotinic acid biosynthesis.The physiological significance of this phenomenon remains obscure, since it is not clear what advantage is gained by the diabetic organism through diverting an intermediate from nicotinic acid synthesis. The mechanism by which hormonal regulation of picolinic carboxylase operates is also not known. It does seem clear, however, that the more general phenomenon of competition for available substrate by different enzymes is exhibited in an extreme form in this system, in which the substrate for a spontaneous reaction is utilized by an enzyme whose activity changes from very low to higher values.