Purification and initial characterization of guinea pig testicular acrosin

Guinea pig (GP) acrosin was purified following acid extraction of testicular acetone powder, pH precipitation of the soluble extract, gel filtration on Sephadex G-100, ion-exchange chromatography on SP-Sephadex, and affinity chromatography on Concanavalin A-Sepharose. Final purification was achieved by re-chromatography on Sephadex G-100. Enzymatic activity was detected by following the hydrolysis of N-benzyloxycarbonylarginyl amide of 7-amino-4-trifluoromethylcoumarin at 37 degrees C, pH 8.0, before and after activation. GP testicular acrosin exhibited a molecular weight of 48,000 by gel filtration and 34,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Following SDS-PAGE in gels containing 0.1% gelatin, protease activity was observed to comigrate with the major protein detected by silver staining. The purified GP acrosin showed cross-reactivity with a monospecific polyclonal rabbit antiserum directed against boar sperm acrosin and exhibited reversible pH-dependent activation. The physiochemical characteristics of the purified protein, including the amino acid composition, resemble those reported for acrosins from other species.     

Preparation of a gap junction fraction from uteri of pregnant rats: the 28-kD polypeptides of uterus, liver, and heart gap junctions are homologous

A procedure for the preparation of a gap junction fraction from the uteri of pregnant rats is described. The uterine gap junctions, when examined by electron microscopy of thin sections and in negatively stained preparations, were similar to gap junctions isolated from heart and liver. Major proteins of similar apparent molecular weight (Mr 28,000) were found in gap junction fractions isolated from the uterus, heart, and liver, and were shown to have highly homologous structures by two-dimensional mapping of their tryptic peptides. An Mr 10,000 polypeptide, previously deduced to be a proteolytic product of the Mr 28,000 polypeptide of rat liver (Nicholson, B. J., L. J. Takemoto, M. W. Hunkapiller, L. E. Hood, and J.-P. Revel, 1983, Cell, 32:967-978), was also studied and shown by chymotryptic mapping to be homologous in the uterine, heart, and liver gap junction fractions. An antibody raised in rabbits to a synthetic peptide corresponding to an amino-terminal sequence of the liver gap junction protein recognized Mr 28,000 proteins in the three tissues studied, showing that the proteins shared common antigenic determinants. These results indicate that gap junctions are biochemically conserved plasma membrane specializations. The view that gap junctions are tissue-specific plasma membrane organelles based on previous comparisons of Mr 26,000-30,000 polypeptides is not sustained by the present results.     

MORPHOLOGY AND LABORATORY CULTIVATION OF ECHINOSTELIUM MINUTUM

Alexopoulos , Constantine J. (State U. Iowa, Iowa City.) Morphology and laboratory cultivation of Echinostelium minutum. Amer. Jour. Bot. 47(1): 37—43. Illus. 1960.—The morphology of the sporangium, spores, swarm cells and Plasmodium of the white form of Echinostelium minutum is described. A peridium is present in the early stages of sporangial formation. It eventually disappears leaving only a small collar at the base of the columella. The structure of the spore wall is unique in this genus. The spore case may be described as consisting of a thin wall with several thickened portions distributed over its surface. These are particularly evident in germinated spores. Spore germination and swarm cells are described for the first time. Swarm cells are biflagellate with two long anterior flagella of nearly equal length. The Plasmodium remains microscopic until fruiting time, when it gives rise to but a single sporangium. The plasmodial protoplast never becomes differentiated into veins but remains more or less homogeneous. It exhibits almost imperceptibly slow, irregular streaming instead of the reversible, rapid, rhythmic motion characteristic of plasmodia of most other Myxomycetes which have been studied. It typifies, therefore, a third type of Plasmodium which may be placed alongside that of the Physarales, and that of Stemonitis flavogenita. The laboratory cultivation of E. minutum from spore to spore on agar media is reported here for the first time.     

THE LABORATORY CULTIVATION OF STEMONITIS

Alexopoulos , Constantine J. (State U. Iowa, Iowa City.) The laboratory cultivation of Stemonitis. Amer. Jour. Bot. 46(2): 140-142. Illus. 1959.—The cultivation of a species of Stemonitis, probably S. flavogenita, in laboratory culture is reported here for the first time. The organism completed its entire life cycle on artificial media from spore to spore, in the presence of contaminating bacteria, in 36 days. The plasmodium, characteristically different from those of the Physarales, is described and illustrated.     

Discrete steps in dioxygen activation—The cytochrome oxidase/O2 reaction

The kinetic constraints that are imposed on cytochrome oxidase in its dual function as the terminal oxidant in the respiratory process and as a redox-linked proton pump provide a unique opportunity to investigate the molecular details of biological O₂ activation. By using flow/flash techniques, it is possible to visualize individual steps in the O₂-binding and reduction process, and results from a number of spectroscopic investigations on the oxidation of reduced cytochrome oxidase by O₂ are now available. In this article, we use these results to synthesize a reaction mechanism for O₂ activation in the enzyme and to simulate time-concentration profiles for a number of intemediates that have been observed experimentally. Kinetic manifestation of the consequences of coupling exergonic electron transfer to endergonic proton translocation emerge from this analysis. Energetic efficiency in this process apparently requires that potentially toxic intermediate oxidation states of dioxygen accumulate to substantial concentration during the reduction reaction.