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101.
102.
From an enrichment culture of white-crystal deposits from aged Cheddar cheese, an atypical Lactobacillus strain was characterized. The new isolate is facultatively heterofermentative, has a G + C content of 40 mol%, and produces D and L isomers of lactic acid. The strain had a limited ability to ferment carbohydrates. It utilized fructose, galactose, glucose, lactose, maltose, mannose, and ribose but was negative for esculin, gluconate, citrate, and several other carbon sources. The isolate also had low DNA-DNA homologies with strains of Lactobacillus casei and Lactobacillus plantarum. Cheese prepared with milk containing the isolate developed white crystals during curing. Formation of copious D-lactate from unknown substrates during curing probably caused the white-crystal deposits. The strain has been deposited in the American Type Culture Collection (ATCC 49178). 相似文献
103.
We calculated the potential H(2) and formate diffusion between microbes and found that at H(2) concentrations commonly found in nature, H(2) could not diffuse rapidly enough to dispersed methanogenic cells to account for the rate of methane synthesis but formate could. Our calculations were based on individual organisms dispersed in the medium, as supported by microscopic observations of butyrate-degrading cocultures. We isolated an axenic culture of Syntrophomonas wolfei and cultivated it on butyrate in syntrophic coculture with Methanobacterium formicicum; during growth the H(2) concentration was 63 nM (10.6 Pa). S. wolfei contained formate dehydrogenase activity (as does M. formicicum), which would allow interspecies formate transfer in that coculture. Thus, interspecies formate transfer may be the predominant mechanism of syntrophy. Our diffusion calculations also indicated that H(2) concentration at the cell surface of H(2)-consuming organisms was low but increased to approximately the bulk-fluid concentration at a distance of about 10 mum from the surface. Thus, routine estimation of kinetic parameters would greatly overestimate the K(m) for H(2) or formate. 相似文献
104.
Youngdo Won Richard A. Friesner Martin R. Johnson Jonathan L. Sessler 《Photosynthesis research》1989,22(3):201-210
The Soret absorption spectra of six synthetic rigid porphyrin dimers whose crystal structures have been determined are simulated using simple exciton theory. The objective is to test the validity of the point dipole and associated approximations; the electronic interaction parameters are thus calculated using data obtained from the monomer spectra, with no adjustable parameters. Satisfactory agreement between theory and experiment is obtained for one class of dimers but not for a second. This poses a challenge for semiempirical electronic structure methods as to whether improvements over the point dipole calculations can be obtained. 相似文献
105.
106.
107.
Binding of a pancreatic nuclear protein is correlated with amylase enhancer activity. 总被引:5,自引:1,他引:4 下载免费PDF全文
The mouse amylase gene Amy-2.2 is expressed at high levels specifically in the acinar cells of the pancreas. The region between -172 and -110 of this gene includes sequence elements common to pancreas-specific genes. Nuclear proteins with specific affinity for this region were partially purified from rat pancreas. The consensus element of another pancreas-specific gene, elastase 1, competes for protein binding to the amylase sequences. Binding was localized by DNase I protection to the sequence -156 to -122. Site-directed mutagenesis of this sequence resulted in concomitant loss of protein binding and enhancer activity. Photo-affinity labelling of pancreatic nuclear extracts identified one predominant binding protein with a molecular weight of approximately 75 kDa. The data indicate that binding of this nuclear protein is essential for the enhancer activity of this pancreas-specific element. 相似文献
108.
The Caenorhabditis elegans genome contains monomorphic minisatellites and simple sequences. 总被引:1,自引:0,他引:1 下载免费PDF全文
Many species have been shown to contain tandemly repeated short sequence DNA known as minisatellites and simple sequence motifs. Due to allelic variation in the copy number of the repeat unit these loci are usually highly polymorphic. Here we demonstrate the presence of sequences in the genome of the nematode Caenorhabditis elegans which are homologous to two sets of short sequence DNA. However, when two independent strains were compared no polymorphism for these sequences could be detected. 相似文献
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110.
Trophoblast/leukocyte-common antigen is expressed by human testicular germ cells and appears on the surface of acrosome-reacted sperm 总被引:5,自引:0,他引:5
The murine monoclonal antibody H316 reacts with a cell-surface antigen of human trophoblast, leukocytes, certain epithelia, and several malignant cell types. We have found that the H316 antibody also recognizes an antigen synthesized by pre- and post-meiotic human testicular germ cells and is expressed in the acrosomal region of methanol-fixed testicular, epididymal, and ejaculated sperm. The antigen is poorly expressed on the surface of fresh ejaculated motile sperm, but is detectable on most viable sperm after a 6-h incubation in medium containing human serum albumin (HSA), or 60-min incubation with the calcium ionophore A23187 (both treatments induce sperm acrosomal changes termed capacitation and acrosome reaction). We found that antigen recognized by H316 is immunoprecipitated as a single, broad 50 kDa band from radiolabeled ionophore-treated sperm extracts and that preincubation of HSA-capacitated sperm with this antibody causes a moderate, but significant, inhibition of hamster egg penetration. These data indicate that the antigen recognized by the H316 monoclonal antibody is synthesized by testicular germ cells and is surface-expressed on capacitated/acrosome-reacted sperm populations. Its potential as a human sperm acrosome reaction marker, and possible biological role in sperm-egg or sperm-lymphocyte interactions, warrants further investigation. 相似文献