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961.
Evolution of oxygen and turnover of cytochromes b-563 and ? were measured upon illumination of isolated intact spinach chloroplasts with a series of flashes. The flash yield of cytochrome ? oxidation approximated the sum of the yields of cytochrome b-563 reduction and electron transfer through Photosystem II, regardless of whether HCO?3, 3-phosphoglycerate or O2 served as the terminal electron acceptor. No absorbance contribution from cytochrome b-559 was discerned within the time range studied. Some pseudocyclic electron flow occurred when both HCO?3 and 3-phosphoglycerate were omitted, and possibly also during induction of photosynthesis; however, the flash yield data suggest that O2 is not reduced at a significant rate during steady state photosynthesis. The maximum rate of cytochrome ? turnover (1000 μequiv./mg chlorophyll per h) was adequate to support the highest rates of photosynthesis observed in isolated chloroplasts.These results agree with the concept that cytochrome ? is a component both of the linear and cyclic pathways whereas cytochrome b-563 functions only in the cyclic pathway. NH4Cl decreased the half time of cytochrome b-563 oxidation from 11.6 to 8.2 ms and decreased the half time of cytochrome ? reduction from 7.2 to 2.8 ms. The cyclic and linear pathways thus seem to be jointly regulated by a transthylakoid H+ gradient through a common control point on the reducing side of cytochrome ?. Cyclic turnover also increased during the induction phase of photosynthesis, when linear throughput is limited by the rate of utilization of NADPH. The slow rise in the P-518 transient correlated with increased cyclic activity under the above conditions.It is proposed that flexibility in the utilization of linear and cyclic pathways allows the chloroplast to generate ATP and NADPH in ratios appropriate to varying needs. 相似文献
962.
A protein spot corresponding to l-glycerol-3-phosphate dehydrogenase (α-GPDH, E.C. 1.1.1.8, NAD+ oxidoreductase) has been identified on a two-dimensional gel (isoelectric focusing-SDS gel) containing up to 150 stained protein spots from a crude Drosophila homogenate. Preliminary identification of the α-GPDH spot was made by including a suitable amount of purified Drosophila α-GPDH in crude fly homogenates prior to electrophoresis and observing an intensity enhancement of the corresponding protein spot on the gels. When three purified electrophoretic variants (slow, fast, and ultrafast) were mixed and analyzed by two-dimensional gel electrophoresis, horizontal displacements of the three protein spots were observed. Immunoprecipitation of the enzyme prior to electrophoresis and gene mapping further confirmed the identity of the α-GPDH protein spot. The α-GPDH spot can also be detected by autoradiography of a two-dimensional gel from a single fly extract, where it has been estimated to constitute 0.5–1% of the total soluble protein. Mutants which express no apparent α-GPDH activity were analyzed by two-dimensional gels and immunoelectrophoresis in an attempt to identify and characterize the inactive proteins. It is suggested that these techniques provide a powerful tool for the analysis of CRM+-null activity mutants of a specific gene-enzyme system. 相似文献
963.
964.
Susan Schenck Theodore Chase Jr. W. D. Rosenzweig David Pramer 《Applied microbiology》1980,40(3):567-570
A number of species of nematode-trapping fungi, which capture and digest nematodes having keratin and collagen in their cuticles, were tested for the ability to produce extracellular collagenase and keratinase. Collagenase, which is active on ichthyocol, earthworm collagen, and procollagen from chicken embryo fibroblasts, was found in the growth medium of all tested species; keratinase was not found. The enzyme from Arthrobotrys amerospora was concentrated by precipitation with (NH4)2SO4 and further purified by adsorption on collagen at 0°C. The collagenase was active over a pH range of 2.5 to 10.0. It was not inactivated by dialysis against ethylenediaminetetraacetic acid for 48 h or by the sulfhydryl group inhibitors N-ethylmaleimide and p-chloromercuribenzoate. The production of collagenase may aid the fungus to penetrate the cuticle of its prey. 相似文献
965.
An improved method is described for the resolution of enantiomeric isopropyl esters of N-trifluoroacetyl-α-amino acids of nonbasic amino acids using N-docosanoyl-l-valyl-t-butylamide and N-octadecanoyl-l-valyl-l-valine cyclohexyl ester as mixed chiral phases on 150-ft stainless-steel capillary columns. Enantiomers of Ala, Val, Ile, Leu, Ser, Thr, Asp, Met, Glu, and Phe are resolved in 105 min. This method avoids the fractionation problems and high costs encountered with the diastereometric method and difficulties and costs encountered in loading and maintaining glass capillary columns. It is particularly useful for studies involving a large number of resolutions as in a study of the kinetics of racemization of amino acids. 相似文献
966.
Anti-idiotypic antibodies against TEPC-15 myeloma protein (BALB/c origin) were raised in allogeneic animals by immunization of A/J mice with the myeloma protein. The antibody activities were fractionated into two specificities by TEPC-15 immunoadsorbent affinity columns by elution with free hapten (phosphorylcholine, PC), followed by elution with acidic buffer (glycine- HCl, pH 2.3). Idiotype binding analysis indicated that the fraction eluted with hapten could be inhibited in its binding to TEPC-15 by free hapten (i.e., binding site-directed anti-idiotypic antibody), whereas the acid-eluted fraction could not (i.e., framework-directed anti-idiotypic antibody). When analyzed for their biological activities on PC-specific B lymphocytes producing T-15 idiotype-bearing antibodies, both anti-idiotypic antibody fractions had similar suppressive effects on the in vitro production of antiphosphorylcholine antibody in culture. 相似文献
967.
968.
The closely related fern generaHemionitis L. andGymnopteris Bernhardi are separated primarily on differences in leaf architecture and venation. Studies indicate that these characters are highly variable and unreliably diagnostic. Further, the type species of the two genera readily hybridize with each other. Spore morphology, as exhibited by SEM, does not support the traditional alignment of the species in these two genera: some species ofHemionitis andGymnopteris have the same rugose to papillate spores, while other species from both genera possess crested spores. The flavonoid chemistry of these taxa coincides with spore type, i.e., taxa from both genera which possess crested spores produce kaempferol and quercetin 3-0-glycosides, while species with tuberculate spores produce only quercetin 3,4′-0-glycosides. The spore and chemical data suggest a realignment of these taxa within a single genus, which would avoid the rather tenuous dependence on a single vegetative character for generic distinctions. 相似文献
969.
The husk from the seeds of Plantago ovata Forsk yielded two fractions when exposed to mild aikali, namely, the mucilage polysaccharide (85%, apparently a single species) and the non-polysaccharide component (15%). Methylation analysis and partial hydrolysis with acid showed the mucilage polysaccharide to be a highly branched, acidic arabinoxylan, the xylan backbone having both (1→4) and (1→3) linkages. The majority of the residues in the xylan backbone are variously substituted at O-2 and O-3 with arabinose, xylose, and an aldobiouronic acid identified as 2-O-(galactopyranosyluronic acid)-rhamnose. A structure incorporating these features for the husk polysaccharide is proposed. 相似文献
970.
Mouse epidermal cells express Ia antigens. Epidermal cells from C3H and B10. A mice express I-A and I-E region gene products. Products associated with I-B and I-J were not detectable. A weak reaction was seen with anti-I-C sera. Products of the I-A region appear to be preferentially expressed when compared to I-E-region gene products. Ten percent of epidermal cells possess IgG-specific Fc receptors and 15% of epidermal cells can phagocytize latex particles. Our studies suggest that Ia-positive epidermal cells in mice are not necessarily limited to Langerhans cells. 相似文献