Nucleus chicken liver

Again, DFR from vertebrate sources has the residue Tyr-31 in place of the less less bulky Leu-27 of the bacterial enzymes these residues line the pocket in which the pteridine nucleus has to fit in each case. Vertebrate enzymes, which have about 185 residues, are larger than those of bacteria with about 165 residues. How this difference comes about is seen in chicken liver enzyme which has three extra loops on the edge of the pleated sheet, all of them free from normal interchain hydrogen-bonding (Volz etal., 1982). Unlike bacterial DFR, mammalian DFR can reduce folate as well as dihydrofolate. 

Fig. 1 Ultrastructure of a nucleus from chicken liver and diagrammatic representation of the nuclear envelope. (A) Transmission electron micrograph of an ultrathin section through a nucleus from baby chick (cockerel) liver, showing the perinuclear cytoplasm (Cyt), nuclear envelope (NE), nuclear pore complex (NPC), and nucleoplasm (Nu). Scale bar, 1 /im. (B) Diagram showing prominent features of the nuclear envelope—the lamina (L), inner nuclear membrane (INM), outer nuclear membrane (ONM), nuclear pore complex (NPC), rough endoplasmic reticulum (RER), and ribosomes (R).

Vitamin A is assumed to be contained mainly in the Kupffer cells of the liver. The intracellular distribution of the vitamin has also been studied in chicken liver. Twenty-one per cent of the vitamin is found in the nucleus, 7% in the mitochondria, and 72% in the supernatant. Therefore, the vitamin seems to be concentrated essentially in the supernatant fluid, and the amount of vitamin associated with the nucleus and the mitochondria is probably due to contamination of the fraction by the supernatant vitamin A. This intracellular distribution might be peculiar to the liver— the main site of vitamin A storage therefore, the cellular distribution of the vitamin gives no clue as to its mode of action. The liver vitamin is bound to protein. The protein that is bound to the alcohol derivative of vitamin A is probably different from that bound to the ester derivative of vitamin A. 

Fe- and Mn-containing superoxide dismutases have, moreover, been isolated. They show striking sequence homologies. (Fe)-SOD has mainly been found in prokaryotes. (Mn)-SOD occurs in prokaryotes, (20,000), in the matrix of mitochondria, although encoded by the nucleus, and also in the cytosol of e.g. liver cells (human, chicken in contrast with rat)... 

The cytoplasmic factors that allow the induction of DNA synthesis may have little species specificity. For example, mouse liver nuclei injected into amphibian eggs undergo DNA synthesis (Graham et al., 1966). MammaUan cell cytoplasm can also stimulate the initiation of DNA synthesis in avian nuclei. The nucleus of a mature chicken erythrocyte... 

Humphries et al. (1976) used a sensitive method to hybridize globin mRNA to DNA. Globin RNA sequences were found not only in erythroidal cells but also in the cells of other tissues, i.e., fibroblasts, liver, and brain. In these cells, however, globin mRNA is not transported from the nucleus into the cytoplasm. Thus, there is no Hb synthesis. Therefore, the development of cells with erythroidal characteristics is determined mostly by gene modifiers which act on the post-transcriptional and possibly the translational levels. Knochel and Kohnert-Stavenhagen (1977) found that preparations of nuclear RNA from chicken embryo brain are contaminated with erythrocyte RNA. This RNA composed 0.41% of the total RNA population. Globin mRNA was not found in the cytoplasm of brain cells. 

In 1929, Jones, Phillips, Larsell, and Nokes (65) reported the hematopoietic effect of nuclear extractives in human anemias. They believed that nuclear extractives from various organ sources—considered to be nucleoproteins and the sodium salts of nucleic acids—contained an unknown hematopoietic stimulant. Oral administration of such extractives, prepared from chicken corpuscles, beef spleen, beef liver, beef kidney, beef heart muscle, salmon liver, beef thymus and beef pancreas, in J g. doses, yielded satisfactory results in pernicious as well as other anemias. They thus tentatively concluded that the hematopoietic stimulant is an integral part of the cell nucleus. 

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