Mg2+ is an essential activator of hydrolytic activity of membrane-bound pyrophosphatase of Rhodospirillum rubrum

The substrate for the hydrolytic activity of membrane-bound pyrophosphatase is the PP(i)-Mg2+ complex. The enzyme has no activity when the free Mg2+ concentration is lower than 10 microM (at 0.5 mM-PP(i)-Mg2+), and therefore free Mg2+ is an essential activator of the hydrolytic activity. The Km for the substrate changes in response to variation in free Mg2+ concentration, from 10.25 to 0.6 mM when free Mg2+ is increased from 0.03 to 1.0 mM respectively. The Km for Mg2+ depends on the substrate concentration: the Km decreases from 0.52 to 0.14 mM from 0.25 to 0.75 mM-PP(i)-Mg2+ respectively. The extrapolated Km for Mg2+ in the absence of the substrate is 0.73 mM. Imidodiphosphate-Mg2+ and free Ca2+ were used as competitive inhibitors of substrate and activator respectively. The equilibrium binding kinetics suggest an ordered mechanism for the activator and the substrate: Mg2+ ions bind the enzyme before PP(i)-Mg2+ in the formation of the catalytic complex, membrane-bound pyrophosphatase-(Mg2+)-(PP(i)-Mg2+).

The evaluation of 186Re-labeled antibodies using N2S4 chelate in vitro and in vivo using tumor-bearing nude mice

We have recently described a method for radiolabeling monoclonal antibodies, with metallic radionuclides using a new chelating agent N2S3. Using this chelate the monoclonal antibodies Lym-1 and B72.3 were labeled with 186Re and their biological integrity was evaluated in vitro and in vivo. 186Re-labeled antibodies using N2S4 methodology were found to be stable in human serum and retained their immunoreactivity. Intravenous administration of 0.5 mCi 186Re-labeled antibodies resulted in partial or complete regression of tumor tissue in mice.

Cytoplasmic estradiol binding sites in testis of fertile and infertile men

Free cytoplasmic estradiol receptor was determined in testicular biopsies from six adults showing various primary testicular disorders, and in testicular tissue obtained at autopsy from 18 males of various ages. Estradiol receptors were found in all cases examined. Receptor concentration varied during testicular maturation and from one patient to another. The presence of the receptor at an early stage of development and the changes observed in its concentration during testicular maturation and dysfunction support the idea that estradiol may play, through its receptor interaction, an important role in the regulation of testicular steroidogenesis during postnatal human development.

The inability of in vitro transforming SV40 subgenomes to cause tumors in vivo

Linear or subgenomic SV40 DNAs were transfected into cells from a variety of species (including rodent, dog, muntjak, and monkey) and injected subcutaneously into neonate Syrian hamsters for tumorigenicity testing. The 'early-region' subgenomes were capable of transforming cells in vitro. Complete genomes or complementary subgenomes could transform nonpermissive and semipermissive cells, were infectious for permissive cells, and induced tumors from which infectious virus could be rescued. Tumors were not formed in neonate hamsters upon injection with subgenomic SV40 DNAs, even those capable of transforming cells in vitro. These results suggested that SV40 tumor formation in vivo may require a complete genome.

Bacteroides fragilis resistance to clindamycin in vitro

Clindamycin resistance in Bacteroides fragilis was examined in 507 strains isolated from 1973 to 1981. Three groups were recognized: highly susceptible (minimum inhibitory concentration [MIC] less than or equal to 0.125 microgram/ml), intermediately susceptible (MIC = 0.25 to 4 micrograms/ml), and highly resistant to (MIC greater than or equal to 8 microgram/ml). The incidence of high-level resistance (1.8%) had not changed during this period. Only 8 of 17 isolates reputed to be highly clindamycin resistant that were referred to our laboratory proved to be highly resistant (MICs greater than or equal to 32 microgram/ml), whereas the other 9 were intermediately susceptible. Analysis of 2- and 10-microgram clindamycin disks for determining the susceptibility of B. fragilis revealed a high false-resistance rate with the 2-microgram disk, most errors occurring with the intermediate group. There was no false resistance with the 10-microgram disk. When disk diffusion susceptibility of B. fragilis is employed, we recommend the 10-microgram disk to predict accurately the susceptibility of B. fragilis to clindamycin.

Brain monoamine oxidase activity after in vivo-chronic iprindole treatment

The effects of chronic administration of three different doses of iprindole on the monoamine oxidase activity and neurotransmitter content were studied in the cerebral cortex, the mesencephalon and the cerebellum of mouse brain. The treatment inhibited mitochondrial monoamine oxidase activity of all three brain regions studied, although a dose-response inhibitory effect was found only in the mesencephalon. Brain regional serotonin contents were markedly increased after iprindole treatment. The 5-hydroxyindoleacetic acid contents showed a significant decrease only in the cerebral cortex. Neither dopamine nor norepinephrine brain regional contents were significantly altered. On the basis of these results it is suggested that a substrate-specific inhibition of monoamine oxidase is involved in the mechanism of action of this tricyclic antidepressant.

Glucose metabolism in the testis of the normal and streptozotocin diabetic rat

In the present work, the metabolism of [U-14C]glucose was studied in the testicular tissue of normal and streptozotocin diabetic rats. The results show that diabetes alters 14CO2 production and 14C incorporation into lipids from [U-14C]glucose. No differences were found in the [14C]proteins and [14C]nucleic acids between experimental groups. Results are discussed in relation to an insulin deficiency and/or an alteration in the hypothalamic-hypophyseal-gonadal axis.

The fine structure of the glycocalyx of equine spermatozoa: a high-resolution cytochemical study

Equine spermatozoa were obtained from ejaculates of young stallions. The seminal plasma was removed and the sperm pellets washed three times with 0-15 M-NaCl solution before final centrifugation at 4500 g for 15 min. The pellets were fixed in a mixture of 2-5% glutaraldehyde in 0-1 M-cacodylate buffer, pH 7-4, with 0-5% Alcian blue and post-fixed in 1% osmium tetroxide with 1% lanthanum nitrate; other samples were treated with ruthenium red. All samples were dehydrated in ascending concentrations of ethanol, embedded in araldite and thin sections examined in an electron microscope. Electron dense deposits of lanthanum were present on the surface plasmalemma of the head, mid-piece and tail of 70% of mature spermatozoa, and similar deposits were seen in ruthenium red-treated samples. No glycocalyx was observed in untreated spermatozoa.