Protochlorophyllide b does not occur in barley etioplasts

Barley (Hordeum vulgare L.) etioplasts were isolated, and the pigments were extracted with acetone. The extract was analyzed by HPLC. Only protochlorophyllide a and no protochlorophyllide b was detected (limit of detection < 1% of protochlorophyllide a). Protochlorophyllide b was synthesized starting from chlorophyll b and incubated with etioplast membranes and NADPH. In the light, photoconversion to chlorophyllide b was observed, apparently catalyzed by NADPH :protochlorophyllide oxidoreductase. In darkness, reduction of the analogue zinc protopheophorbide b to zinc 7-hydroxy-protopheophorbide a was observed, apparently catalyzed by chlorophyll b reductase. We conclude that protochlorophyllide b does not occur in detectable amounts in etioplasts, and even traces of it as the free pigment are metabolically unstable. Thus the direct experimental evidence contradicts the idea by Reinbothe et al. (Nature 397 (1999) 80-84) of a protochlorophyllide b-containing light-harvesting complex in barley etioplasts.     

中国不产曲籽芋属植物

曲籽芋属在中国的分布源自对采自海南的一号标本———W.T.Tsang（曾怀德）553=L.U.16052（1927年8月27日采）的错误鉴定。这号标本被E.D.Merrill定名为曲籽芋Cyrtosperma lasioides Griffith,并分藏于国内外的标本馆。因此,《海南植物志》第四卷、《中国植物志》第十三卷第二分册、《中国种子植物科属词典》以及吴征镒的《中国种子植物属的分布区类型》一文等都记录了曲籽芋属。收藏在中国科学院华南植物研究所、英国邱皇家植物园和爱丁堡皇家植物园的W.T.Tsang（     

Enterohepatic circulation of N-acetyl-leukotriene E4

N-Acetyl-leukotriene E4, the end product of leukotriene C4 metabolism in the mercapturic acid pathway, was rapidly eliminated from the blood circulation into the bile of rats. Part of the N-acetyl-leukotriene E4 secreted from bile into the intestine underwent enterohepatic circulation. Leukotriene absorption occurred from the small intestine and from the colon. Biliary and urinary excretion within 5.5 h amounted to 15 and 2%, respectively, of the intraduodenally administered N-acetyl- 3H leukotriene E4 in animals anesthetized with ketamine. HPLC analyses indicated that 35% of the biliary radioactivity corresponded to unchanged N-acetyl-3H leukotriene E4, while 65% in bile and 100% in urine were polar metabolites. Enterohepatic circulation extends the biological half-life of N-acetyl-leukotriene E4.     

Release of neuropeptides does not only occur at nerve terminals

Neurohypophysial hormones are packed in secretory granules which are stored in nerve endings and in dilatations called nerve swellings. Although it was originally believed that the nerve swellings were storage compartments and that release occurred solely from the nerve terminals, the present paper demonstrates that secretion can occur to the same extent from both nerve endings and nerve swellings.     

Skeletal myogenesis in the mouse esophagus does not occur through transdifferentiation

To determine the developmental history of murine esophageal skeletal muscle, smooth muscle cells were fate mapped by lineage-specific recombination and phenotypically marked by eGFP. Examination of embryonic and postnatal tissues revealed that esophageal skeletal muscle does not arise from transdifferentiation of committed smooth muscle cells.     

Parathyroid hormone-induced bone resorption does not occur in the absence of osteopontin

Osteopontin is an RGDS-containing protein that acts as a ligand for the alpha(v)beta(3) integrin, which is abundantly expressed in osteoclasts, cells responsible for bone resorption in osteopenic diseases such as osteoporosis and hyperparathyroidism. However, the role of osteopontin in the process of bone resorption has not yet been fully understood. Therefore, we investigated the direct function of osteopontin in bone resorption using an organ culture system. The amount of (45)Ca released from the osteopontin-deficient bones was not significantly different from the basal release from wild type bones. However, in contrast to the parathyroid hormone (PTH) enhancement of the (45)Ca release from wild type bones, PTH had no effect on (45)Ca release from organ cultures of osteopontin-deficient bones. Because PTH is located upstream of receptor activator of NF-kappaB ligand (RANKL), that directly promotes bone resorption, we also examined the effect of RANKL. Soluble RANKL with macrophage-colony stimulating factor enhanced (45)Ca release from the bones of wild type fetal mice but not from the bones of osteopontin-deficient mice. To obtain insight into the cellular mechanism underlying the phenomena observed in osteopontin-deficient bone, we investigated the number of tartrate-resistant acid phosphatase (TRAP)-positive cells in the bones subjected to PTH treatment in cultures. The number of TRAP-positive cells was increased significantly by PTH in wild type bone; however, no such PTH-induced increase in TRAP-positive cells was observed in osteopontin-deficient bones. These results indicate that the absence of osteopontin suppressed PTH-induced increase in bone resorption via preventing the increase in the number of osteoclasts in the local milieu of bone.     

Recombination between chloroplast DNAs does not occur in sexual crosses of Oenothera

Summary Induction of the SOS genes is required for efficient repair of damaged DNA in Escherichia coli. SOS induction by nalidixic acid or oxolinic acid, two inhibitors of DNA gyrase, requires the RecBC enzyme of E. coli. We report here that the nuclease activity of RecBC enzyme is not needed for SOS induction by these agents. We suggest that the unwinding activity of RecBC enzyme produces single-stranded DNA which activates the RecA protein to stimulate LexA repressor cleavage and SOS induction.     

Genomic hypomethylation is specific for preneoplastic liver in folate/methyl deficient rats and does not occur in non-target tissues

Chronic dietary insufficiency of the lipotropic nutrients choline and methionine is hepatocarcinogenic in male rats and certain mouse strains. Despite the fact that DNA hypomethylation is a hallmark of most cancer genomes, the tissue-specific consequences of this alternation with respect to tumorigenesis remain to be determined. In the present study, the folate/methyl deficient model of multistage hepatocarcinogenesis was used to evaluate in vivo alterations in DNA methylation in the liver, the carcinogenesis target tissue, and in non-target tissues, including pancreas, spleen, kidney, and thymus, of male F344 rats. By utilizing the HpaII/MspI-based cytosine extension assay, we demonstrated that the percent of CpG sites that lost methyl groups on both strands progressively increased in liver tissue after 9, 18, and 36 weeks of folate/methyl deficiency. The endogenous activity of DNA methyltransferase in liver of rats fed with folate/methyl deficient diet for the 36-week period gradually increased with time. In contrast, non-target tissues displayed no changes in DNA methylation level or activity of DNA methyltransferase. The failure of DNA methyltransferase to restore and maintain DNA methylation patterns in preneoplastic liver tissue may lead to the establishment of tumor-specific DNA methylation and DNA methyltransferase profiles that are not expressed in normal liver. These results provide additional information about alterations in DNA methylation during early preneoplastic stages of carcinogenesis. They also demonstrate that DNA hypomethylation is localized to tissue that undergoes carcinogenesis, and is not altered in non-target tissues.     

Arginine synthesis does not occur during first-pass hepatic metabolism in the neonatal piglet

We have shown that first-pass intestinal metabolism is necessary for approximately 50% of whole body arginine synthesis from its major precursor proline in neonatal piglets. Furthermore, the intestine is not the site of increased arginine synthesis observed during dietary arginine deficiency. Primed constant intravenous (iv) and intraportal (ip) infusions of L-[U-14C]proline, and iv infusion of either L-[guanido-14C]arginine or L-[4,5-3H]arginine were used to measure first-pass hepatic arginine synthesis in piglets enterally fed either deficient (0.20 g.kg(-1).day(-1)) or generous (1.80 g.kg(-1).day(-1)) quantities of arginine for 5 days. Conversion of arginine to other urea cycle intermediates and arginine recycling were also calculated for both dietary treatments. Arginine synthesis (g.kg(-1).day(-1)) from proline was greater in piglets (P < 0.05) fed the deficient arginine diet in both the presence (generous: 0.07; deficient: 0.17; pooled SE = 0.01) and absence (generous: 0.06; deficient: 0.20; pooled SE = 0.01) of first-pass hepatic metabolism. There was no net arginine synthesis from proline during first-pass hepatic metabolism regardless of arginine intake. Arginine conversion to urea, citrulline, and ornithine was significantly greater (P < 0.05) in piglets fed the generous arginine diet. Calculated arginine fluxes were significantly lower (P = 0.01) for [4,5-3H]arginine than for [guanido-14C]arginine, and the discrepancy between the values was greater in piglets fed the deficient arginine diet (35% vs. 20%). Collectively, these findings show that first-pass hepatic metabolism is not a site of net arginine synthesis and that piglets conserve dietary arginine in times of deficiency by decreasing hydrolysis and increasing recycling.     

Enterohepatic circulation of N-acetyl-leukotriene E4

N-Acetyl-leukotriene E₄, the end product of leukotriene C₄ metabolism in the mercapturic acid pathway, was rapidly eliminated from the blood circulation into the bile of rats. Part of the N-acethyl-leukotriene E₄ secreted from bile into the intestine undewent enterohepatic circulation. Leukotriene absorption occurred from the small intestine and from the colon. Biliary and urinary excretion within 5.5 h amounted to 15 and 2%, respectively, of the intraduodenally administered N-acetyl- H leukotriene E₄ in animals anesthetized with ketamine. HPLC analyses indicated that 35% of the biliary radioactivity corresponded to unchanged N-acetyl- H leukotriene E₄, while 65% in bile and 100% in urine were polar metabolites. Enterohepatic circulation extends the biological half-life of N-acetyl-leukotriene E₄.     

Toll-like receptor 2-dependent bacterial sensing does not occur via peptidoglycan recognition

Toll-like receptor 2 (TLR2) has been shown to recognize several classes of pathogen-associated molecular patterns including peptidoglycan (PG). However, studies linking PG with TLR2 recognition have relied mainly on the use of commercial Staphylococcus aureus PG and have not addressed TLR2 recognition of other PG types. Using highly purified PGs from eight bacteria (Escherichia coli, Pseudomonas aeruginosa, Yersinia pseudotuberculosis, Helicobacter pylori, Bacillus subtilis, Listeria monocytogenes, Streptococcus pneumoniae and S. aureus), we show that these PGs are not sensed through TLR2, TLR2/1 or TLR2/6. PG sensing is lost after removal of lipoproteins or lipoteichoic acids (LTAs) from Gram-negative and Gram-positive cell walls, respectively. Accordingly, purified LTAs are sensed synergistically through TLR2/1. Finally, we show that elicited peritoneal murine macrophages do not produce tumour necrosis factor-alpha or interleukin-6 in response to purified PGs, suggesting that PG detection is more likely to occur intracellularly (through Nod1/Nod2) rather than from the extracellular compartment.     

Evidence that short-term regulation of nodule permeability does not occur in the inner cortex

Regulation of nodule permeability in response to short-term changes in environmental and physiological conditions is thought to occur by occlusion of intercellular spaces in the nodule inner cortex. To test this hypothesis, the permeability of legume nodules was altered by adapting them to either 20 or 80% O₂ over a 2.5-h period. The nodules were then rapidly frozen, cryo-planed and examined under cryo-scanning electron microscopy for differences in the number, area or shape factor of intercellular spaces. Comparisons were made between whole nodules and specific nodule zones (outer cortex, middle cortex, inner cortex and central zone) in each treatment. Gas analysis measurements indicated that nodules equilibrated at 20% O₂ had a 6.6-fold higher permeability than those equilibrated at 80% O₂ However, no significant differences were observed between pO₂ treatments in the number of open intercellular spaces, the cross-sectional area of those spaces, or the proportion of the tissue area present as open space in whole nodules or any nodule zone. Also, although nodules in both treatments possessed a boundary layer of tightly packed cells in the inner cortex, the total area of intercellular spaces between cells bordering this layer did not differ between treatments. Together these observations do not support the currently favored hypothesis that nodule permeability is regulated by opening or occlusion of intercellular spaces in the nodule inner cortex. Highly significant differences (P= 0.0006) were observed between O₂ treatments in the shape factor of the open intercellular spaces in all nodule zones. Nodules equilibrated at 80% O₂ had significantly more isodiametric spaces while those equilibrated at 20% O₂ had more long, narrow spaces. This observation suggests that the critical step in the regulation of nodule permeability to O₂ may be localized in the central, infected zone and involve changes in the ratio of the surface area of the intercellular space to the volume of the infected cell.     

Nucleolar dominance does not occur in root tip cells of allotetraploid Brassica species.

Using in situ hybridization and silver staining methods, the numbers of active and inactive rDNA loci have been established for three allotetraploid species of Brassica (B. napus, B. carinata, and B. juncea) and their diploid ancestors (B. campestris, B. nigra, and B. oleracea). The allotetraploid species have chromosome numbers equal to the sum of the numbers in their diploid relatives, but have fewer rDNA loci. All species investigated have lower numbers of active NORs (AgNORs, nucleolar organizer regions) compared with the numbers of rDNA sites revealed by in situ hybridization. The number of active rDNA loci of the allotetraploid species is equal to the number of AgNORs in their diploid ancestors, indicating the absence of nucleolar dominance in amphidiploid Brassica species, at least in root meristematic cells.     

Ribosomal gene amplification does not occur in the oocytes of Locusta migratoria

It has been suggested that Locusta migratoria amplifies its ribosomal RNA genes in the growing oocytes (Kunz (1967) Chromosoma20, 332–370). Cloned ribosomal DNA of L. migratoria was used to analyze rDNA structure and number. The rDNA is localized on three chromosome pairs in six nucleolus organizers. It was found that all structural variants of the rRNA genes which have been described previously are represented in the same relative amounts in DNA from isolated oocytes as in somatic cells. Furthermore, the rRNA gene number is not increased in oocyte DNA, i.e., amplification does not occur. Therefore, the large number of multiple nucleoli seen in the growing oocytes has to be interpreted as the fully extended and fully active set of chromosomal rRNA genes. The total rRNA gene number was determined by dot blot hybridization to be about 3300 genes/haploid genome.     

Enterohepatic circulation in hamsters with an extracorporeal bile duct.

The present study describes a novel technique for investigations of the enterohepatic circulation in the hamster with an extracorporeal bile duct that allows long-term bile collection in the free-moving animal. The animals recovered for 7 days after the operation before the external loop was cut and bile was collected over a period of 78 h. Under these optimal conditions, initial bile flow (651 +/- 89 microliters per 100 g.h-1) and the secretion rates of biliary lipids were several-fold higher than reported in an earlier study using the acute fistula hamster. Biliary cholesterol secretion amounted to 369 +/- 32 nmol per 100 g.h-1, phospholipid secretion was 2.6 +/- 0.3 mumol per 100 g.h-1, and total bile acid secretion was 31.9 +/- 2.2 mumol per 100 g.h-1. A clearcut diurnal rhythm was demonstrated for bile flow and all biliary constituents. After 9 h the depletion of the bile acid pool was complete and cholic acid synthesis derepressed 1.4-fold from a basal rate of 818 nmol per 100 g.h-1, whereas the derepression of chenodeoxycholic acid synthesis was even less pronounced. Biliary cholesterol output increased 2.2-fold, but the phospholipid secretion was constant during the full experiment. It may be concluded that the technique of an extracorporeal bile duct in the free-moving animal allows studies of bile secretion under optimal conditions. Most likely the bile secretion rates given above approach the physiological rates in the hamster.     

Initiation of adenovirus DNA replication does not occur via a hairpin mechanism.

Models have been proposed suggesting that initiation of adenovirus DNA replication might occur via a hairpin mechanism. A consequence of the models is a covalent linkage of progeny and parental DNA in newly completed molecules. Analysis of mature molecules from KB cells infected with adenovirus type 5 indicates that, if a hairpin mechanism is involved, the length of the hairpin must be shorter than 50 basepairs long. Recent nucleotide sequence analysis of the termini of adenovirus type 5 DNA (P.H.Steenbergh et al. (1977) Nucl. Acids Res. 4, 4371-4389) has shown that a hairpin of this size does not exist and that therefore a hairpin mechanism is unlikely.