Block of hamster fertilization by anti-ovary antibody.

Antibody produced in rabbits against hamster ovary blocked fertilization of golden hamster eggs in vitro by binding to the surface of the zona pellucida and rendering it impenetrable to spermatozoa. The antibody was also effective in blocking fertilization in vivo. An intraperitoneal injection of the antibody into females resulted in the complete inhibition of fertilization for approximately 12 days, i.e. three oestrous cycles. This temporary sterility was apparently due to the binding of the antibody to the zona pellucida of oviducal and ovarian oocytes, and dot due to a failure of sperm ascent or capacitation in the female genital tract. Neither the oestrous cycle nor ovulation was affected by the antibody injection.     

Hypoxanthine enhances hydroxyurea-induced sister-chromatid exchanges in Chinese hamster ovary cells

Treatment with 1 mM hydroxyurea (HU) for 12 h induced sister-chromatid exchange (SCE) in CHO-K1 cells. The induced SCE frequency was always higher in cells grown in Ham's F12 medium than in those grown in RPMI 1640 medium. It was shown that hypoxanthine (Hyp), a component of Ham's F12, was to a great extent responsible for producing a higher level of HU-induced SCEs were synergistically enhanced when Hyp was added to RPMI 1640 medium supplemented with dialyzed fetal bovine serum at a concentration of 30 μM, which is the concentration in Ham's F12 medium.

The radioactivity of [¹⁴C]Hyp was readily incorporated into DNA in either the presence or the absence of HU. The greater part was in the forms of dGMP and dAMP. It was not clear whether Hyp was incorported in the form of dIMP or not. Deoxyguanosine (dGuo), but not deoxyadenosine (dAdo) reversed both the incorporation of radioactivity into DNA and the SCE-enhancing effect of Hyp. Our results indicate that incorporation of Hyp into the dNTP pools and into the DNA, together with perturbation of dGuo metabolism under abnormal conditions during and after HU treatment, is involved in the enhancement by Hyp of HU-induced SCEs.     

Purification and properties of two acid phosphatases from midgut glands of abalone Haliotis discus.

Midgut glands of abalone Haliotis discus contained two acid phosphatases [orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2] separable by phosphocellulose column chromatography. They were designated as acid phosphatases I and II in order of elution and were purified 99- and 290-fold, respectively. Purified acid phosphatase II was nearly homogeneous as judged by polyacrylamide gel electrophoresis. The substrate specificity of acid phosphatase I was narrow, whereas that of acid phosphatase II was broad. Good substrates for acid phosphatase I included p-nitrophenyl phosphate, phosphoenolpyruvate, inorganic pyrophosphate, and nucleoside di- and triphosphates. The acid phosphatases did not require any metal ion for maximum activity and were inhibited by Zn2+, Cu2+ and Hg2+. Fluoride and arsenate were potent inhibitors of both enzymes. The pH optima of acid phosphatases I and II were 5.9 and 5.5, respectively. The molecular weights of acid phosphatases I and II were estimated to be 28,000 and 100,000, respectively, by gel filtration on Sephadex G-100. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggested that acid phosphatase II consists of two identical subunits.     

Studies on the dynamic properties of terrestrial ecosystems based on a simulation model II. Tropical rainforest dynamics and stability as influenced by stem mortality

Further analysis of tropical rainforest dynamics and stability in relation to stem mortality has been conducted using a microcomputer model developed in a previous study (Oikawa, 1985). By simulation experiments covering a period of 100 years, the effects of changing stem mortality (δc) upon a tropical rainforest were investigated. Increasing stem mortality ranging from a standard value (3%yr⁻¹) to a 4-fold value (12%yr⁻¹) brings about decreases in stem biomass and thus total living biomass, and a contrasting increase of stem litterfall flux at the steady state of the forest ecosystem. At the same time, the decreased stem biomass at the steady state is predicted to result in increases of gross production (P _g) and net production (P _n), and an improvement in production efficiency of the model rainforest expressed as theP _n/P_g ratio. similar simulation experiments predict that the improved production efficiency in the forest with a 4-fold stem mortality is able to enhance tolerance to less productive environments such as a prolonged dry season or a reduced incident light flux density. On the other hand, the standard stem mortality (δ_c=3%yr⁻¹), which was estimated as a probable value for the Pasoh forest, West Malaysia, is considered to approximate the lower threshold necessary for attaining forest stability. Based on the results obtained, the significance of δ_c for the dynamics and stability of a tropical rainforest ecosystem is discussed in relation to the competition and tolerance of trees. In addition, the effectiveness of the simulation approach adopted here is emphasized. Titles are tentative translations by the author for original titles in Japanese.     

Mitochondrial DNA repair by photolyase.

Photolyase genes of Saccharomyces cerevisiae and Escherichia coli were expressed in S. cerevisiae and photoreactivation in nuclei and mitochondria of the host cells was analyzed by determination of survival and petit rates. Yeast photolyase was able to repair mitochondrial DNA effectively, whereas E. coli photolyase could reduce only a small fraction of the petit rate produced by UV irradiation. Analysis using fusion between yeast photolyase and E. coli lacZ genes as well as a chimeric gene between yeast and E. coli photolyase genes suggests the importance of the protruding amino terminal region of the yeast photolyase for its transport into mitochondria. A significant similarity between the protruding amino termini of yeast photolyase and yeast uracil-DNA-glycosylase suggests a common functional importance of the terminal sequences for both DNA repair enzymes.