Purification and characterization of peptic fragments derived from the carboxyl-terminal half of human albumin

Utilizing a combination of conventional and affinity-chromatographic procedures, we have purified four fragments of human albumin that were generated by controlled limited proteolysis with pepsin [0.3 mM albumin; 37°C; 10 min; pH 3.51; 4.2 mM octanoate; pepsin/albumin, 1:1000 (w/w)]. These fragments have a molecular weight range of 9200-17,000 Da. Amino acid compositions, N- and C-terminal sequences, molecular weights, and other internal markers were used to determine the location of these fragments within the parent molecule. All of the fragments were shown to be derived from the C-terminal half of human albumin. The presence of multiple pepsin-sensitive bonds near the C terminus of each fragment complicated the assignment of specific residue numbers to each fragment. Two pairs of similar peptides were identified: (A) those corresponding to a single-loop structure (residues 309–380 and 309–387) and (B) those containing multiple loops and intraloop cleavages [residues 309–(491–495) with 408–423 deleted]. Purification of these fragments without disulfide bond reduction confirms portions of the loop structure of human albumin and demonstrates increased susceptibility of two specific regions of the C-terminal half of the molecule to peptic digestion.     

Photoresponses of the copepod Mesocyclops edax

The predatory copepod Mesocyclops edax is an important componentof many zooplankton communities where it typically makes extensivedid vertical migrations. To describe the effect of light onadults we measured their photoresponses in the laboratory. Theresponse spectrum is characterized by a wide plateau of greatestsensitivity from about 480 – 580 nm. These animals areadapted to perceive light during the day since their regionof maximum sensitivity overlaps the spectral region of highestquantal intensity underwater (575 – 700 nm). The thresholdintensity for positive phototaxis by dark adapted animals wasabout 5 x 10^–1 Wm^–2 at 540 nm, and they were positivelyphototactic up to an intensity of 5 x 10^–1 Wm^–2.Above this intensity phototaxis is no longer observed. Light-adaptedanimals were less sensitive than dark-adapted, but their generalpattern of response to light intensity did not differ. Thereis no rhythm in phototaxis. Their photoresponses may providea mechanism for controlling vertical migration so as to minimizeexposure to planktivorous fish. ¹Contribution No. 1375-AEL from UM-CEES, Appalachian EnvironmentalLaboratory.     

Enriched populations of rat retinal ganglion cells: Studies using a cell-type specific surface marker

Cells dissociated from adult and neonatal rat retinas were separated by density gradient centrifugation. Previous work had shown that rat retinal cells labelled by an immunofluorescence assay for the Thy-1 antigen were chiefly or exclusively ganglion cells, and so the proportion of Thy-1 positive cells in the density gradient fractions was used as an index of the enrichment of ganglion cells. The proportion of Thy-1 positive neonatal cells was increased from about 0.4% in the initial dissociate to about 8% in the most enriched fraction of a Percoll step gradient. Amongst adult cells the initial 0.7% Thy-1 positive cells were increased to roughly 2% in the best fraction of a metrizamide step gradient.

The presence of relatively large numbers of Thy-1 positive cells in other fractions suggested that it would be difficult to further increase the proportion of rat ganglion cells by methods based on their sedimentation properties. These results demonstrate the importance of cell-type specific markers in attempts to purify cells from the central nervous system.     

Mating strategy shifts in male green treefrogs (Hyla cinerea): An experimental study

Four field experiments were designed to study calling and satellite mating strategies in the green treefrog, Hyla cinerea. (1) The calling male was removed from 19 satellite associations and 11 of the 19 satellite males began calling. (2) After the calling male was removed from 10 satellite associations, a speaker broadcast synthetic mating calls. All of the satellite males oriented to the speaker. (3) Synthetic mating calls were played back to 14 calling males. Eleven males stopped calling and oriented to the speaker during at least one trial. (4) Sequences of synthetic mating calls and synthetic encounter calls were broadcast to 12 calling males. Nine males became satellites when the speaker emitted mating calls; none did so when encounter calls were presented.     

Intertidal distribution of infauna in a central California lagoon: the role of seasonal blooms of macroalgae

This study examined the roles of seasonal blooms of green algae, Ulva expansa (Setchell) Setchell et Gardner, and biotic disturbance by burrowing ghost shrimp, Callianassa gigas Dana, and foraging rays, on the intertidal distributions of a phoronid, Phoronopsis viridis Hilton, and a tellinid bivalve, Macoma nasuta (Conrad). Algal removal experiments in 1984 and 1986 demonstrated that heavy seasonal algal cover in the lower zone significantly reduced the abundances of both Phoronopsis and Macoma. Growth of Macoma transplanted into the algal zone was significantly lower in plots with algal cover than in plots regularly cleared of algae. Algal cover did not significantly affect early recruitment of either Phoronopsis or Macoma. Neither ghost shrimp nor rays appeared to reduce the abundances of phoronids or clams, although ray disturbance did result in a significant increase in the proportion of phoronids regenerating dorsal body parts. These results indicate that seasonal algal blooms are capable of producing discrete patterns of infaunal distribution in intertidal sedimentary habitats.     

The 165-kDa DNA topoisomerase I from Xenopus laevis oocytes is a tissue-specific variant.

Two forms of topoisomerase I can be purified from Xenopus laevis. A protein with a molecular mass of 165 kDa has been identified as topoisomerase I in ovaries (Richard and Bogenhagen, 1989. J. Biol. Chem. 264, 4704-4709). When a similar purification is performed using liver tissue, topoisomerase I is purified as a 110-kDa protein. Separate rabbit antisera were raised against oocyte and liver topoisomerase I polypeptides. Each antiserum reacts in immunoblotting or immunoprecipitation procedures only with the tissue-specific topoisomerase I polypeptide against which it was generated. The failure of the antiserum raised against liver topoisomerase I to cross-react with the oocyte enzyme suggests that the smaller topoisomerase I is not derived from the 165-kDa oocyte enzyme by proteolysis. X. laevis tissue culture cells lysed and processed in the presence of SDS contain the 110-kDa form of topoisomerase I. The 165-kDa form of topoisomerase I disappears during oocyte maturation in vitro.