Trophic interactions in soils as they affect energy and nutrient dynamics. IV. Flows of metabolic and biomass carbon

Flows of biomass and respiratory carbon were studied in a series of propylene-oxide sterilized soil microcosms. One-half of the microcosms received three pulsed additions of 200 ppm glucose-carbon to mimic rhizosphere carbon inputs. Biotic variables were: bacteria (Pseudomonas) alone, or amoebae (Acanthamoeba) and nematodes (Mesodiplogaster) singly, or both combined in the presence of bacteria.Over the 24-day experiment, respiration was significantly higher in the microcosms containing the bacterial grazers. Biomass accumulation by amoebae was significantly higher than that by nematodes. The nematodes respired up to 30-fold more CO₂ per unit biomass than did amoebae. Similar amounts of carbon flowed into both respiratory and biomass carbon in microcosms with fauna, compared with the bacteria-alone microcosms. However, partitioning of available carbon by the microfauna varied considerably, with little biomass production and relatively more CO₂-C produced in the nematode-containing microcosms. The amoebae, in contrast, allocated more carbon to tissue production (about 40% assimilation efficiency) and correspondingly less to CO₂.     

Higher activity of 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) coincides with lower background levels of 8-oxo-2'-deoxyguanosine in DNA of fetal compared with maternal mouse organs.

Mammalian homologues of Escherichia coli MutT, a protein having 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) activity, are thought to play the same role in preventing the incorporation of promutagenic 8-oxo-2'-deoxyguanosine (8-oxo-dG) into DNA. One could thus expect that higher activity of 8-oxo-dGTPase should correlate with a lower background level of 8-oxo-dG in nuclear DNA. During transplacental carcinogenesis experiments, in control healthy Swiss mice on day 18 of gestation we found consistently lower levels of 8-oxo-dG in DNA in fetal livers and lungs (1.74+/-0.04 SE and 1.49+/-0.08 SE 8-oxo-dG/10(5) dG, respectively; pooled organs of fetuses of 8 dams) as compared with maternal organs (3.05+/-0.20 SE and 3.08+/-0.17 SE 8-oxo-dG/10(5) dG, respectively; n = 8). The 8-oxo-dGTPase activity determination in the same organs revealed that the lower levels of 8-oxo-dG in fetal DNA did, indeed, coincide with higher 8-oxo-dGTPase activity (48.8+/-2.6 SE and 52.5+/-2.5 SE U/mg protein in livers and lungs, respectively); and vice versa, higher 8-oxo-dG levels in DNA of maternal organs were associated with lower levels of 8-oxo-dGTPase activity (24.3+/-1.3 SE and 4.7+/-0.6 SE U/mg protein, as above). Without excluding other reasons for the relatively low 8-oxo-dG background in DNA of fetal tissues (e.g., higher level of antioxidants and antioxidative enzymes; more efficient DNA repair), this inverse relationship may support or at least does not contradict the concept of a guardian role of 8-oxo-dGTPase against 8-oxo-dGTP mutagenicity in mammalian cells.     

Affinity chromatography on anti-B1 monoclonal gels for purification and characterization of protein B1 from Escherichia coli ribonucleotide reductase

Affinity gels were prepared from four monoclonal antibodies against the B1 protein of ribonucleotide reductase of Escherichia coli. The gels were used to purify protein B1 and also to study some of its properties. Gels from the nonneutralizing monoclonal anti-B1-k bound as much as 2 mg of B1/mL and were employed to prepare essentially pure B1 protein in a single step from extracts of wild-type E. coli and strains overproducing the subunit. However, B1 prepared from wild-type extracts had a lowered specific activity, suggesting some denaturation during elution of the protein from the column. Addition of the allosteric effector dATP during affinity chromatography changed the chromatographic pattern. Some protein B2, the second subunit of the reductase, remained in all cases bound to the gels together with B1. The gel prepared from anti-B1-c retained two additional proteins. In other experiments involving binding of proteolytic fragments of B1 to various antibodies, we also found a striking effect of dATP, suggesting that dATP made protein B1 less accessible to proteolysis. In these experiments fragments around 15K still had the ability to bind monoclonals, making possible more detailed investigations of the structural contacts between B1 and the monoclonals.