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.     

Non-Decarboxylating transformation of indol-3-ylacetic acid in apple seeds

An enzyme extract from apple(Pyrus malus Borb.) seeds which causes the disappearance of free indol-3-ylacetic acid (IAA) requires the presence of oxygen, but is not inhibited by cyanide. Using 1-¹⁴C-IAA it has been demonstrated that the IAA transformation is not accompanied by its decarboxylation. Decarboxylating IAA oxidase is absent during the whole period of apple seed cold stratification. Free IAA has not been detected in dormant apple seeds and in seeds stratified at low temperature. It appears during stratification at 25 °C. Ethyl ester of IAA and indol-3-ylacetyl aspartate have been identified in dormant and after-ripened seeds. Exogenous 1-¹⁴C IAA taken up by apple embryos is converted into conjugates with aspartate and short peptides containing an aspartate moiety.     

Hydrogen cyanide and embryonal dormancy in apple seeds

Embryos of apple ( Malus domestica Borh. cv. Antonówka) were treated with 1 m M gaseous HCN for 6 h and cultured under a 12 h photoperiod. HCN pretreatment stimulated germination, increased the length of hypocotyls, shortened the main root and decreased the percentages of seedlings with asymmetrically grown as well as with asymmetrically greened cotyledons. High activity of β-cyanoalanine synthase (EC 4.4.1.9) and a sharp increase in cyanogen content during embryo culture suggested very low levels of endogenous HCN. despite the activity of HCN releasing enzymes. The obtained data allow us to postulate an important role for cyanide in the regulatory complex controlling dormancy in apple seeds. Experiments with respiratory inhibitors indicated, however, that HCN pretreatment affected neither the alternative electron transport pathway nor residual respiration.     

The effect of fish predation on Cyclops life cycle

Two populations of Cyclops abyssorum tatricus studied in neighbouring alpine lakes in Tatra Mountains (southern Poland) differed in their life cycles. In the lake with planktivorous fishes, Cyclops was typically monocyclic, with highly synchronized reproduction during two winter months, while in the fishless lake its reproduction was asynchronous and continued for six months. Direct and indirect effects of fish predation on Cyclops life cycles are discussed.     

Cytochromec oxidase fromParacoccus denitrificans in Triton X-100: Aggregation state and kinetics

Cytochromec oxidase fromParacoccus denitrificans was homogenously dispersed in Triton X-100. Using gel exclusion chromatography and sucrose gradient centrifugation analysis a molecular weight of the detergent-protein complex of 155,000 was determined. After subtraction of the bound detergent (111 mol/mol hemeaa ₃) a molecular weight of 85,000 resulted, which agreed well with the model of a monomer containing two subunits. This monomer showed high cytochromec oxidase activity when measured spectrophotometrically in the presence of Triton X-100 (V _max=85 s^–1). The molecular activity, plotted according to Eadie-Hofstee, was monophasic as a function of the cytochromec concentration. AK _m of 3.6×10^–6 M was evaluated, similar to theK _m observed in the presence of dodecyl maltoside [Naeczet al. (1985).Biochim. Biophys. Acta 808, 259–272].     

Potentiation of antitumor effects of tumor necrosis factor α and interferon γ by macrophage-colony-stimulating factor in a MmB16 melanoma model in mice

The efficacy of systemic infusion of recombinant human macrophage-colony-stimulating factor (M-CSF) in combination with local treatment with human recombinant tumor necrosis factor (TNF) and mouse recombinant interferon (IFN) was studied in vivo on a subclone of B16 melanoma (MmB16) in mice. Short-term intravenous administration of M-CSF at a dose of 10⁶ units daily had no antitumor effect in vivo. Similarly, local treatment of tumor with TNF (5 g daily) did not produce any therapeutic effect. However, simultaneous administration of the same dose of TNF with IFN (1000 units daily) resulted in a synergistic effects manifested by the retardation of tumor growth. Addition of systemic infusion of M-CSF to the local therapy with TNF and IFN induced further augmentation of antitumor efficacy and delayed progression of MmB16 melanoma. The strengthened antitumor effect of combination therapy including M-CSF, TNF and IFN was most probably due to the increased release of monocytes from the bone marrow, their recruitment into the site of tumor growth and subsequent local stimulation of their antitumor activity.