Reward partitioning in Capparis spp. along ecological gradient

Summary The genus Capparis is represented in Israel by three taxons of the section spinosa. The pollinators of the three taxa are hawkmoths, crepuscular bees of the genus Proxylocopa and various daily bees. However, the efficiency of the different pollinators is very varied with respect to the individual taxons. Hawkmoths were frequently observed as pollinators of C. spinosa var. aravensis and C. ovata, but rarely on C. spinosa var. aegyptia. All the other bees, on the other hand, were found abundantly on all three taxons, all over the country. The three taxa all provide different rewards for their particular pollinators. Bees visiting C. spinosa var. aegyptia are provided with a lot of pollen but a relatively small amount of nectar, with a low sugar content. C. spinosa var. aravensis and C. ovata (the flowers visited more by hawkmoths), have less pollen but a higher amount of nectar which has a higher concentration of sugar. In drier habitats the emphasis of the reward provided by the flowers is nectar, whilst in the Mediterranean habitats it is the pollen which is the reward, without any connection to the systematic origin of the plant.     

Estimation of symbiotically fixed nitrogen in field grown soybeans: An application of natural15N/14N abundance and a low level15N-tracer technique

Summary Plants from agricultural and natural upland ecosystem were investigated for¹⁵N content to evaluate the role of symbiotic N₂-fixation in the nitrogen nutrition of soybean. Increased yields and lower δ¹⁵N values of nodulating soybeansvs, non-nodulating isolines gave semi-quantitative estimates of N₂ fixation. A fairly large discrepancy was found between estimations by δ¹⁵N and by N yield at 0 kg N/ha of fertilizer. More precise estimates were made by following changes in plant δ¹⁵N when fertilizer δ¹⁵N was varied near¹⁵N natural abundance level. Clearcut linear relationships between δ¹⁵N values of whole plants and of fertilizer were obtained at 30 kg N/ha of fertilizer for three kinds of soils. In experimental field plots, nodulating soybeans obtained 13±1% of their nitrogen from fertilizer, 66±8% from N₂ fixation and 21±10% from soil nitrogen in Andosol brown soil; 30%, 16% and 54% in Andosol black soil; 7%, 77% and 16% in Alluvial soil, respectively. These values for N₂ fixation coincided with each corresponding estimation by N yield method. Other results include: 1)¹⁵N content in upland soils and plants was variable, and may reflect differences in the mode of mineralization of soil organics, and 2) nitrogen isotopic discrimination during fertilizer uptake (δ¹⁵N of plant minus fertilizer) ranged from −2.2 to +4.9‰ at 0–30 kg N/ha of fertilizer, depending on soil type and plant species. The proposed method can accurately and relatively simply establish the importance of symbiotic nitrogen fixation for soybeans growing in agricultural settings.     

Identification with Monoclonal Antibodies of a Second Antigenic Domain on Avena Phytochrome that Changes upon Its Photoconversion

An enzyme-linked immunosorbent assay that revealed an antigenic difference between the red-absorbing and far-red-absorbing forms of phytochrome (Pr and Pfr, respectively) near its amino terminus (Cordonnier M-M, H Greppin, LH Pratt 1985 Biochemistry 24: 3246-3253) was used to screen eight additional monoclonal antibodies directed to phytochrome from etiolated oats. While six of these antibodies detected Pr and Pfr with equal affinity, two of them, designated Oat-9 and Oat-16, bound to Pfr 1.6 to 2.3 times better than to Pr. Competitive enzyme-linked immunosorbent assays indicate (a) that Oat-9 and Oat-16 probably bind to the same domain on phytochrome and (b) that this domain is at least 3.5 nanometers away from the epitope near its amino terminus that was shown earlier to change upon phototransformation. Neither the absorbance spectra of Pr and Pfr, nor the rate of dark reversion of Pfr to Pr, was influenced by the presence of Oat-9. Immunoblotting of sodium dodecyl sulfate polyacrylamide gels after electrophoretic separation of phytochrome fragments obtained by endogenous proteolytic digestion indicates that Oat-16 binds to an epitope located on the chromophore half of this chromoprotein. The observation that the epitope recognized by Oat-9 and Oat-16 is also present on at least some of the immunochemically distinct phytochrome that is obtained from green oat shoots (Shimazaki Y, LH Pratt 1985 Planta 164: 333-344), together with the evidence that this epitope undergoes a change upon photoransformation, indicates that it may play an important role in phytochrome function.     

Hyoscyamine 6beta-hydroxylase, a 2-oxoglutarate-dependent dioxygenase, in alkaloid-producing root cultures

Root cultures of various solanaceous plants grow well in vitro and produce large amounts of tropane alkaloids. Enzyme activity that converts hyoscyamine to 6β-hydroxyhyoscyamine is present in cell-free extracts from cultured roots of Hyoscyamus niger L. The enzyme hyoscyamine 6β-hydroxylase was purified 3.3-fold and characterized. The hydroxylation reaction has absolute requirements for hyoscyamine, 2-oxoglutarate, Fe²⁺ ions and molecular oxygen, and ascorbate stimulates this reaction. Only the l-isomer of hyoscyamine serves as a substrate; d-hyoscyamine is nearly inactive. Comparisons were made with a number of root, shoot, and callus cultures of the Atropa, Datura, Duboisia, Hyoscyamus, and Nicotiana species for the presence of the hydroxylase activity. Decarboxylation of 2-oxoglutarate during the conversion reaction was studied using [1-¹⁴C]-2-oxoglutarate. A 1:1 stoichiometry was shown between the hyoscyamine-dependent formation of CO₂ from 2-oxoglutarate and the hydroxylation of hyoscyamine. Therefore, the enzyme can be classified as a 2-oxoglutarate-dependent dioxygenase (EC 1.14.11.-). Both the supply of hyoscyamine and the hydroxylase activity determine the amounts of 6β-hydroxyhyoscyamine and scopolamine produced in alkaloid-producing cultures.     

Isolation of a surface glycoprotein from Myxococcus xanthus.

The isolation of a glycoprotein from vegetative cells of Myxococcus xanthus is reported. The protein, abbreviated VGP, was first identified during a survey of surface proteins as a major protein that could be radioiodinated in vegetative, but not developing, cells (P.Y. Maeba, J. Bacteriol. 155:1033-1041, 1983). The protein was extracted from membranes with Triton X-100 and subsequently purified by DEAE-cellulose chromatography, chromatofocusing, and gel filtration. The protein has an Mr of approximately 74,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an isoelectric point of 3.2 to 3.3. The carbohydrate moiety which made up approximately 13.5% of the weight of the VGP comprised primarily neutral sugars and smaller amounts of hexosamines and uronic acids. The amino acid content revealed no unusual features, but analysis by the method of Barrantes (F. Barrantes, Biochem. Biophys. Res. Commun. 62:407-414, 1975) indicated it is likely a peripheral membrane protein. The protein makes up approximately 1% of the total cell protein and is a prominent surface structure. Because glycoproteins have been implicated in cellular interactions in a number of systems, the VGP may play an important role in the social behavior exhibited by M. xanthus.     

A Zn2+-dependent and histone H1-specific protease in sea urchin sperm

Protease activity was extracted from sea urchin sperm with 1% Triton X-100 and partially purified by DEAE-cellulose and Sephadex G-100 chromatography. The enzyme preferentially degraded histone H1, while showing only a weak activity toward other histones. Heat-denatured casein and bovine serum albumin were not digested by this enzyme under the present experimental conditions. This protease hydrolyzed only Boc-Val-Leu-Lys-MCA among various peptidyl-MCAs. The optimal pH ranged from 7 to 11. Its molecular weight was about 41,000. Among various known inhibitors of proteases, only omicron-phenanthroline effectively inhibited the activity. The enzyme was stimulated by Zn2+ or Co2+. It was inactivated by omicron-phenanthroline but could be reactivated by the addition of Zn2+ or Co2+. Therefore, this protease seems to be a metalloprotease dependent on Zn2+ or Co2+. The insensitivity of this enzyme to phosphoramidon and its very restricted substrate specificity suggest that this enzyme is very different from other metalloproteases described hitherto.     

Isolation, and catalytic and immunochemical properties of cathepsin D-like acid proteinase from rat erythrocytes

An erythrocyte membrane-associated cathepsin D-like acid proteinase, termed "EMAP," was purified to homogeneity from freshly collected rat blood in a yield of 60-65%. The molecular weight of the enzyme was determined to be 80,000-82,000 by Sephadex G-100 gel filtration. The enzyme was inhibited strongly by pepstatin and partially by HgCl2, Pb(NO3)2, and iodoacetic acid. The preferred substrate for the enzyme was hemoglobin. The enzyme also hydrolyzed serum albumin and casein, but to lesser extents, with an optimum pH of 3.5-4.0. However, it could not hydrolyze leucyl-2-naphthylamide, benzyloxycarbonyl-Phe-Arg-4-methyl-7-coumarylamide or other synthetic substrates at pH values ranging from 3.5 to 9.5. The enzyme was very similar to human EMAP in a number of enzymatic properties, whereas it differed from rat cathepsin D in several respects, such as pH stability, molecular weight, isoelectric point, and chromatographic properties. Immunologically, the enzyme cross-reacted with the rabbit antibody prepared against human EMAP. The patterns of immunoelectrophoresis, immunoblotting, and immunoprecipitation of the enzyme were remarkably similar, if not identical, to those of human EMAP. In contrast, rat EMAP showed no reaction with the rabbit antibody raised to rat spleen cathepsin D. These results indicate that EMAP is a unique cathepsin D-like acid proteinase different from ordinary cathepsin D.     

Epidermal growth factor increases c-myc mRNA without eliciting phosphoinositide turnover, protein kinase C activation, or calcium ion mobilization in Swiss 3T3 fibroblasts

Incubation of quiescent cultures of Swiss 3T3 cells with epidermal growth factor (EGF) caused an increase in c-myc mRNA. Under these conditions, EGF did not induce phosphoinositide turnover, formation of diacylglycerol, formation of inositol tris-, bis-, and monophosphates, protein kinase C activation, or Ca2+ mobilization. Although it has been reported that both protein kinase C and Ca2+ may be responsible for the platelet-derived growth factor- and fibroblast growth factor-induced increases in c-myc mRNA in Swiss 3T3 cells (Kaibuchi, K., Tsuda, T., Kikuchi, A., Tanimoto, T., Yamashita, T., & Takai, Y. (1986) J. Biol. Chem. 261, 1187-1192), these results indicate that neither protein kinase C nor Ca2+ is involved in the EGF-induced increase in c-myc mRNA, and that an unidentified system may be involved in this reaction.     

Kinetics of the hydrolysis of monodispersed dihexanoyllecithin catalyzed by the phospholipase A2 from Agkistrodon halys blomhoffii venom

The hydrolysis of 1,2-dihexanoyl-sn-glycero-3-phosphorylcholine (diC6PC), catalyzed by the phospholipase A2 from the venom of Agkistrodon halys blomhoffii, was studied at 25 degrees C and the ionic strength of 0.1 in the presence of 3-33.3 mM Ca2+, which can saturate the Ca2+-binding site of the enzyme. The initial velocity data, obtained at various concentrations of the substrate below the critical micelle concentration (cmc), were analyzed according to the Michaelis-Menten equation. The pH-dependence curve of the Km value exhibited only one transition below pH 8. The analytical results indicated that the pK value of 6.30 of an ionizable group changed to 6.54 on the binding of the monodispersed substrate. This ionizable group was assigned as the alpha-amino group on the basis of its pK value, which had been determined from the pH dependence of the binding constant of monodispersed n-dodecylphosphorylcholine (n-C12PC) (Ikeda and Samejima (1981) J. Biochem. 90, 799-804, and Haruki et al. (1986) J. Biochem. 99, 99-109). The pH-dependence curve of the kcat value exhibited two transitions, below pH 6.5 and above pH 9.5. The analytical results indicated the participation of two ionizable groups with pK values of 5.55 and 10.50. Deprotonation of the former and protonation of the latter group were found to be essential for the catalysis. The former ionizable group was assigned as His 48 in the active site on the basis of its pK value, which had been determined from the pH dependence of the binding constant of Ca2+ (Ikeda et al. (1981) J. Biochem. 90, 1125-1130).(ABSTRACT TRUNCATED AT 250 WORDS)