Dihydroorotase from Escherichia coli. Purification and characterization

Dihydroorotase (4,5-L-dihydroorotate amidohydrolase (EC 3.5.2.3], which catalyzes the reversible cyclization of N-carbamyl-L-aspartate to dihydro-L-orotate, has been purified to homogeneity from an over-producing strain of Escherichia coli. Treatment of 70 g of frozen cell paste produces about 7 mg of pure enzyme, a yield of about 35%. The native molecular weight, determined by equilibrium sedimentation, is 80,900 +/- 4,300. The subunit molecular weight, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis is 38,400 +/- 2,600, and by amino acid analysis is 41,000. The enzyme is thus a dimer and contains 0.95 +/- 0.08 tightly bound zinc atoms per subunit when isolated by the described procedure, which would remove any loosely bound metal ions. Isoelectric focusing under native conditions yields a major species at isoelectric point 4.97 +/- 0.27 and a minor species at 5.26 +/- 0.27; dihydroorotase activity is proportionately associated with both bands. The enzyme has a partial specific volume of 0.737 ml/g calculated from the amino acid composition and a specific absorption at 278 nm of 0.638 for a 1 mg/ml solution. At 30 degrees C, the Michaelis constant and kcat for dihydro-DL-orotate (at pH 8.0) are 0.0756 mM and 127 s-1, respectively; for N-carbamyl-DL-aspartate (at pH 5.80), they are 1.07 mM and 195 s-1.     

Influence of canopy opening on the environment and herb layer in a northern hardwoods forest

Single- (33–37 m²) and multi-tree (51–151 m²) gaps were created in an Allegheny Plateau northern hard-woods forest to investigate environmental and herb layer response to canopy opening. After gap creation, noon light on clear summer days was brightest north of opening center. At other times of the day, and when skies were overcast, there was no difference in the light quantity beneath opened and closed canopy. Nor was the distribution of soil moisture or of soil or air temperature greatly affected by gap creation. Species establishment tended to be higher near opening centers; otherwise, there was no pronounced effect of canopy opening on plant cover or species richness during the first four years after gap creation. Biotic responses were not significantly correlated with any environmental factor.     

Amino acid sequence of rabbit ventricular myosin light chain-2: Identity with the slow skeletal muscle isoform

Many studies have established a correlation of differences in the activities of various muscle types with differences in the expression of myosin isoforms. In this paper we report the sequence determination of myosin light chain-2 from rabbit slow skeletal (LC2s) and ventricular (LC2v) nmscles. We sequenced tryptic peptides from LC2v which account for all except a few terminal amino acid residues. The major part (87 residues) of the rabbit LC2s sequence, obtained from tryptic and cyanogen bromide (CNBr) peptides, was found to be identical to rabbit LC2v. Our results provide the first sequence information on LC2s from any species, and lend strong support to the hypothesis that LC2s and LC2v are identical. Comparisons of rabbit LC2v and LC2s with rabbit LC2f (from fast skeletal muscle), and also with chicken LC2f and LC2v, show clearly that LC2s and LC2v from mammalian and avian species are more closely related to each other than they are to LC2f isoforms from the same species.     

In vivo fluorescence excitation and absorption spectra of marine phytoplankton: I. Taxonomic characteristics and responses to photoadaptation

Absorption and fluorescence excitation spectra were measuredfor batch cultures of five species of marine phytoplankton grownunder high and low light. These spectra were examined for propertiescharacteristic of taxonomic position and of photoadaptive response.While regions of absorption and excitation of chlorophyll afluorescence diagnostic of pigment composition were identifiable,photoadaptive response had greater influence on spectral variability.Although reduced growth irradiance caused changes in both theabsorption and fluorescence excitation spectra, the fluorescenceexcitation spectrum appears to be more sensitive to alterationsin the ambient light field for growth than does the absorptionspectrum. For a single species. the fluorescence excitationspectrum for a sample grown at low irradiance showed greaterstructure than that for the sample grown at a high irradiance.Under low light conditions, the excitation of chlorophyll afluorescence by accessory pigments increased relative to theexcitation by chlorophyll a itself The highest fluorescenceyields occur in the blue-green region of the spectrum, correspondingto bands of peak absorption by the accessory pigments. Changesin absorption spectra are less marked, but two features recur.First. in the blue-green region of the spectrum from -500–560nm. absorption is enhanced in the low-light cells relative tothat of the high-light cells. Second, the ratio of absorptionat 435 nm to that at 676 nm was greater for the high-light cells.Correlating changes in pigment concentrations were observed.The influence of photoadaptation on the properties of fluorescenceexcitation spectra is as great or greater than the influenceof pigment complements characteristic of specific algal taxa.     

Menstrual cycle patterns of hormones and sexual behavior in gorillas

Oppositely sexed pairs of gorillas were tested behaviorally during the menstrual cycle to determine the relationship between hormone concentrations of the female and the frequency of sexual activity by the pair. Five females were tested individually during two cycles with each of two males, but serum samples for hormone assay were obtained from each female only during the first cycle of testing. There was no clear relationship between hormones and behavior for the single cycle in which the serum samples were obtained, with the exception that no copulations occurred after the early luteal phase, when progesterone was greater than 5 ng/ml. Normalized behavioral data from all four test cycles for all pairs suggested that female-solicited copulations were restricted primarily to the periovulatory period. Male sexual initiative (by one of the males) accounted for most copulations temporally dissociated from the periovulatory period. Normalized hormone data for all of the females suggested that (1) attractivity was associated with estradiol concentrations during the follicular phase, (2) proceptivity with estradiol and testosterone at midcycle, whereas (3) receptivity was not associated with hormone patterns or cycle phase. The data suggest that hormones are one of several variables that contribute to the regulation of sexual behavior in gorillas.     

Studies on the Indochina I/CDC strain of Plasmodium falciparum in Colombian and Bolivian Aotus monkeys and different anophelines

The Indochina I/CDC strain of Plasmodium falciparum was isolated from a physician returning to the United States after working in the refugee camps along the Thailand-Kampuchean border. The strain was established in splenectomized Aotus monkeys from Colombia after being grown in vitro for 50 days. During the first three passages in Colombian monkeys, the parasites were not infective to Bolivian Aotus monkeys. After six intervening passages in Saimiri sciureus monkeys, the parasites produced high parasitemias in both Colombian and Bolivian Aotus, but gametocytes were no longer produced. Mosquito infections were obtained only during the first three passages in the Colombian monkeys. The most susceptible mosquito was Anopheles freeborni, followed by An. dirus, An. stephensi, An. maculatus, An. culicifacies, and, rarely, An. gambiae. Sporozoites were found in the salivary glands of the An. freeborni, An. dirus, An. stephensi, and An. maculatus.     

Studies of the Sal I strain of Plasmodium vivax in the squirrel monkey (Saimiri sciureus)

The Sal I strain of Plasmodium vivax was successfully adapted to three phenotypes of the squirrel monkey, Saimiri sciureus. Through five linear blood passages, parasitemias in excess of 200,000/mm3 blood were attained; Bolivian phenotype Saimiri appear to develop higher peak parasitemias. Sporozoites of the Sal I strain inoculated intravenously produced patent parasitemias in all five squirrel monkeys challenged, with prepatent periods ranging from 21 to 38 days. Anopheles freeborni and An. gambiae were the most susceptible of eight anopheline species fed on infected squirrel monkeys. As a model for in vivo studies of P. vivax the Sal I strain in Saimiri has great potential.