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241.
The fat body of developing mid- and late fourth instar larvae of a midge, Chironomus thummi, has been investigated by means of the benzidine reaction for the localization of haemoglobin within cells. In the subepidermal fat body the reaction deposits of the haemoglobin pseudo-peroxidase activity appear predominantly in the intracisternal cavities of ER and the Golgi, and later, in the pharate pupal stage, in small dense granules (0.5–1 μm in. diameter).All the major protein bands of fat body extracts, which are resolved in electrophoresis, give the benzidine reaction and show incorporation of 14C-amino levulinic acids, in this case a specific marker for haemoglobin synthesis. In addition, labelled proteins show identical electrophoretic mobility as the haemoglobins of the haemolymph, suggesting that haemoglobins are synthesized in the fat body. Two types of fat body cells seem to differ with respect to their rôle in haemoglobin metabolism. 相似文献
242.
Photosynthetically fixed 14C was analyzed in various chemical fractions from leaves and stems of cottonwood (Populus deltoides Bartr. ex. Marsh.) during dormancy induction. Dormancy was induced by 8-h photoperiods and 20/14°C temperature regimes. Within 4 weeks under short days, terminal buds were set and leaf expansion and stem elongation had stopped. 14C2 was fed to a leaf at Leaf Plastochron Index 7 for 30 min. Either after this 30 min feeding period or after a 48-h translocation period the plants were sampled, freeze-dried, extracted and analyzed for14C. 14C-fixation decreased during dormancy induction from 60% to 17% of the 3.7 MBq 14C applied at 0 week and 8 weeks, respectively. Percentage distribution of 14C in chemical fractions of source leaves reflected leaf age and translocation inhibition. In rapidly growing plants, considerable 14C was incorporated into leaf protein while most of the soluble14C-sugars were either metabolized or translocated out of the leaf. After terminal bud set, the percentage of 14C in the protein and residue fractions decreased rapidly and that in the sugar fraction increased. Percent distribution in stems closely reflected changing metabolic pathways of carbon flow as influenced by dormancy induction. For example, the 14C in structural carbohydrates decreased in 5 weeks under short days from 65 to less than 10% of the 14C recovered in the chemical fractions, thus indicating cambium inhibition. At the same time the percentage of 14C in starch and sugar increased indicating storage. Short term (after 30 min) incorporation of 14C into the protein and starch fractions of leaves changed relatively little throughout the 8-week induction period. In contrast the turnover rates of these fractions (14C present after 48 h) increased considerably after active growth of the whole plant stopped. 相似文献
243.
244.
Barbara R. Hough-Evans Marcelo Jacobs-Lorena Michael R. Cummings Roy J. Britten Eric H. Davidson 《Genetics》1980,95(1):81-94
Comparative measurements are presented of the sequence complexity of the RNA stored in the eggs of two dipteran flies, Musca domestica and Drosophila melanogaster. The genome of Musca is about five times the size of the Drosophila genome and contains about 3.6 times as much single-copy sequence. As shown earlier, the interspersion of repetitive and single-copy sequence is of the short-period form in Musca, and is of the long-period form in Drosophila. The egg RNA complexities were determined by hybridization of excess RNA with radioactively labeled single-copy DNA. Complexity is expressed as the length (in nucleotides) of diverse single-copy sequence represented in the RNA. The complexity of the RNA of the Musca egg is about 2.4 x 107 nucleotides, and that of the Drosophila egg is about 1.2 x 107 nucleotides. The RNA of the Musca egg is similar to or very slightly lower in complexity than that of other egg RNAs, e.g., those of Xenopus and sea urchin. Compared to all previously measured egg RNAs, Drosophila egg RNA is low in sequence complexity. 相似文献
245.
Abstract— Acetylcholinesterase (AChE) and pseudocholinesterase (°ChE) were studied in vivo and during the first several months of development of pectoral and posterior latissimi dorsi (PLD) muscles in normal and dystrophic chickens. Muscle extracts were prepared in a high ionic strength-nonionic detergent medium in the presence of protease inhibitors, in order to obtain complete solubilization and to prevent degradation of intrinsic molecular forms of both enzymes. In both normal and dystrophic pectoral muscles levels of AChE and °ChE increase rapidly in vivo, °ChE accounting for 5–10% of total cholinesterase activity. In the normal pectoral muscle the concentration of both enzymes drops rapidly after hatching with increasing muscle mass; total AChE per muscle remains relatively constant for 30 days post-hatch. In the dystrophic pectoral muscle both AChE and °ChE accumulate after hatching, resulting in greatly elevated levels (approx 10–25-fold) of both enzymes throughout the period studied. Multiple molecular forms of AChE and °ChE are observed in the pectoral muscle by sucrose gradient centrifugation. Four principal forms are distinguished: two light (L1, L2), one medium (M), and one heavy (H2). The °ChE forms are 0.5–1.0 S units lighter than the corresponding AChE forms. L2 is the predominant light form of AChE, whereas L1 is the major light °ChE form detected. The lighter forms of AChE predominate in normal and dystrophic embryonic pectoral muscle at day 14, being replaced by the H2 form by day 19. H2 is the major °ChE form detected at day 19. After hatching, H2 AChE is the predominant form found in both of the normal muscles studied. In the dystrophic pectoral muscle, progressive accumulation of the L2 form of AChE is detected as early as day 4 post-hatch; this form eventually becomes predominant, although the heavier forms are also elevated. In PLD muscle the same phenomenon occurs, but with a slower time course. In dystrophic pectoral muscle a similar rise in the L1 form of °ChE is first observed by day 4, with heavier forms also elevated in the mature muscle. Thus the alteration in the control of these two enzymes in dystrophic fast-twitch muscles results in an accumulation of the light forms of AChE and °ChE. 相似文献
246.
Protoplasts of the filamentous green alga Mougeotia sp. are spherical when isolated and revert to their normal cylindrical cell shape during regeneration of a cell wall. Sections of protoplasts show that cortical microtubules are present at all times but examination of osmotically ruptured protoplasts by negative staining shows that the microtubules are initially free and become progressively cross-bridged to the plasma membrane during the first 3 h of protoplast culture. Cell-wall microfibrils areoobserved within 60 min when protoplasts are returned to growth medium; deposition of microfibrils that is predominantly transverse to the future axis of elongation is detectable after about 6 h of culture. When regenerating protoplasts are treated with either colchicine or isopropyl-N-phenyl carbamate, drugs which interfere with microtubule polymerization, they remain spherical and develop cell walls in which the microfibrils are randomly oriented. 相似文献
247.
Samuel H. Barondes Eric C. Beyer Wayne R. Springer Douglas N. Cooper 《Journal of cellular biochemistry》1981,16(3):233-242
Endogenous lectins in both cellular slime molds and chicken tissues have been localized primarily intracellularly, in contrast with the predominantly extracellular localization of the glycoproteins, glycolipids, and glycosaminoglycans with which they might interact. Here we present evidence that lectins in both of these organisms may be externalized and become associated with the cell surface and/or extracellular materials. In chicken intestine, chicken-lactose-lectin-II is shown to be localized in the secretory granules of the goblet cells, along with mucin, and to be secreted onto the intestinal surface. In embryonic muscle, chicken-lactose-lectin-I is shown to be externalized with differentiation, ultimately becoming localized on the surface of myotubes and in the extracellular spaces. In a cellular slime mold, Dictyostelium purpureum, externalization of lectin is elicited by either polyvalent glycoproteins that bind the small amount of endogenous cell surface lectin, or by slime mold or plant lectins that bind unoccupied complementary cell surface oligosaccharides. These results suggest that externalization of endogenous lectin may be a response to specific external signals. We conclude that lectins are frequently held in intracellular reserves awaiting release for specific external functions. 相似文献
248.
Lymphocytes from chickens homozygous (B
2
B
2) at the major histocompatibility complex (MHC) were tested for cytotoxic activity against five types of target chicken embryo fibroblasts (CEF). Lymphocytes from B2B2 chickens bearing RSV-induced tumors lysed in vitro targets of B
2
B
2 and B
5
B
5 RSV-infected CEF and B
5
B
5 normal CEF, but did not lyse B
2
B
2 and B
24
B
24 normal CEF. Lymphocytes from normal B
2
B
2 chickens did not lyse any of the five types of CEF targets. Alloantisera absorption studies showed that both RSV-infected and uninfected CEF shared alloantigens, in particular B-F alloantigens, with syngeneic erythrocytes. Absorption with B
2
B
2 RSV-infected CEF significantly lowered the titer of B
2
B
2 anti-B
5
B
5 alloantisera. Cross-reactivity between B
5 antigen(s) and tumor-associated antigen was suggested and the nature of the cross-reactivity was discussed. It is hypothesized that this cross-reactivity prevents B
5
B
5 chickens from recognizing RSV-induced tumors as foreign, enhances tumor growth and leads to death of the host. 相似文献
249.
Cysteine metabolism has been thought to be important to the phenomenon of dimorphism inHistoplasma capsulatum. We sought mutants with genetic blocks in the metabolism of cysteine by selection of colonies resistant to the toxic analogue, selenocystine. The 22 resistant strains thus obtained were all deficient in uptake of cystine from the surrounding medium but were normally able to convert from mycelium to yeast and back again. Furthermore, they had normal quantities of NADH-dependent cystine reductase when this enzyme was measured. We conclude that mutants defective in cystine uptake can be readily obtained by selection of colonies resistant to selenocystine, and that a lesion in cystine-uptake does not appear to affect the phenomenon of dimorphism in this organism.Preliminary reports of this work were presented at the Second International Congress of Mycology, Tampa, 1977 and at the first International Conference on Histoplasmosis, Atlanta, 1978. 相似文献
250.
RNase activity from Chlorella was partially purified. Two RNase activities were demonstrated, one soluble and the other ribosomal. The effects on ribonuclease activity of variations in pH and temperature, and of Mg2+, Na+, and mononucleotides were examined. The RNase activities (phosphodiesterases EC 3.1.4.23) were both endonucleolytic, releasing oligonucleotides, and cyclic nucleotide intermediates, but exhibited different specificities in releasing mononucleotides from RNA. The ribosomal activity released 3′-GMP, and after prolonged incubation 3′-UMP, but the soluble activity released 3′-GMP, 3′-AMP and 3′-UMP. Neither ofthe RNase preparations hydrolysed DNA, nor released 5′-nucleotides from RNA. Increased ribosomal RNase activity was related to dissociation of ribosomes, and latency of ribosomal RNase activity was demonstrated. The possible in vivo distribution of RNases is discussed. 相似文献