Modelling basic features of specificity in the binding of a dicationic steroid diamine to double-stranded oligonucleotides.

An investigation of the intrinsically preferred binding modes of a steroid diamine, dipyrandium, to the double-stranded hexanucleotides d(TATATA)2, d(ATATAT)2, and d(CGCGCG)2 is carried out by the energy minimization procedure JUMNA. Several alternative binding modes are compared: groove binding in which the conformation of the oligonucleotide remains close to that of B-DNA, intercalation between base-pairs and interaction with variously kinked structures in which base pairs of dinucleoside steps open towards the groove in which the binding occurs. The favored binding configuration occurs at the d(TpA) step of the AT kinked nucleotides in which the kink opens the base pairs towards the minor groove. Thus, for the d(T1A2T3A4T5A6)2 sequences the preferred complexation involves the kink at the T3A4 step facing the cyclohexane rings A, B, and C of the ligand. For the d(A1T2A3T4A5T6)2 sequence, the kink occurs at the T2A3 step facing the cationic pyrrolidine ring linked to ring A. The binding of dipyrandium to d(CGCGCG)2 is found to be considerably less favourable than for either of the two (AT) sequences.     

Electrostatic and steric control of electron self-exchange in cytochromes c, c551, and b5.

The ionic strength dependence of the electron self-exchange rate constants of cytochromes c, c551, and b5 has been analyzed in terms of a monopole-dipole formalism (van Leeuwen, J.W. 1983. Biochim. Biophys. Acta. 743:408-421). The dipole moments of the reduced and oxidized forms of Ps. aeruginosa cytochrome c551 are 190 and 210 D, respectively (calculated from the crystal structure). The projections of these on the vector from the center of mass through the exposed heme edge are 120 and 150 D. For cytochrome b5, the dipole moments calculated from the crystal structure are 500 and 460 D for the reduced and oxidized protein; the projections of these dipole moments through the exposed heme edge are -330 and -280 D. A fit of the ionic strength dependence of the electron self-exchange rate constants gives -280 (reduced) and -250 (oxidized) D for the center of mass to heme edge vector. The self-exchange rate constants extrapolated to infinite ionic strength of cytochrome c, c551, and b5 are 5.1 x 10(5), 2 x 10(7), and 3.7 x 10(5) M-1 s-1, respectively. The extension of the monopole-dipole approach to other cytochrome-cytochrome electron transfer reactions is discussed. The control of electron transfer by the size and shape of the protein is investigated using a model which accounts for the distance of the heme from each of the surface atoms of the protein. These calculations indicate that the difference between the electrostatically corrected self-exchange rate constants of cytochromes c and c551 is due only in part to the different sizes and heme exposures of the two proteins.     

Differences in growth of transplantable ascites hepatoma among various lines of Donryu rat

A total of 48 Donryu rats from 8 colonies of 5 lines were inoculated intravenously with 10(7) cells of the ascites hepatoma strain AH 66. All the conventional rats of the lines D-1 and D-2 died between 9 and 15 days after inoculation with a good growth of implanted tumor cells. On the other hand, SPF rats of the lines A-1, B-1, C and E survived for 60 days showing complete rejection of the implanted tumor cells. A 50% of conventionalized ex-SPF rats of the lines A-2 and B-2, which had been once established as SPF colonies, and thereafter had been "re-conventionalized", rejected the tumor cells. The present observations indicate that the microbial conditions of the animal, e.g. whether the animal is SPF or not, might play an important role in the growth of the implanted ascites hepatoma.     

Ca2+ channels in chick neural retina cells characterized by 1,4-dihydropyridine antagonists and activators

The voltage-sensitive calcium channel in cultured chick neural retina cells was characterized by the actions of the enantiomers of Bay K 8644 and 202-791 and other 1,4-dihydropyridines. These cells showed time- and voltage-dependent Ca2+ uptake that was stimulated by K+ depolarization and blocked by the inorganic calcium channel blockers Cd2+ and Co2+. A small fraction only (15% maximum) of the uptake was inactivated by predepolarization of the cells with 80 mM K+. Ca2+ uptake was sensitive to the 1,4-dihydropyridine calcium channel antagonists and activators. (S)-Bay K 8644 and (S)-202-791 stimulated the Ca2+ uptake, and (R)-Bay K 8644 and (R)-202-791 as well as nitrendipine and PN 200-110 inhibited Ca2+ uptake stimulated by K+ depolarization or channel activators. The K+ depolarization-stimulated uptake was inhibited by 90%, but the activator-stimulated uptake was completely blocked by the 1,4-dihydropyridine antagonists. The potencies of these agents as inhibitors of Ca2+ uptake were significantly lower than the binding affinities in membrane preparations from the same cells or their binding and pharmacologic affinities in vascular smooth muscle. K+ depolarization or (S)-Bay K 8644 induced 45Ca2+ uptake was not observed in a glial cell culture. [3H]Nitrendipine and [3H]PN 200-110 bound to membrane preparations of the cells consistent with the presence of a single type of high affinity binding site.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phosphorylation of avian retrovirus matrix protein by Ca2+/phospholipid-dependent protein kinase

The matrix protein from avian myeloblastosis virus and the Rous sarcoma virus, Prague C strain, is a phosphoprotein. A comparison of the amino acid sequences shows these phosphoproteins are very similar. The sites of phosphorylation of the matrix protein purified from virions are identified as serine residues 68 and 106. Treatment with purified rabbit skeletal-muscle protein phosphatase 1 or 2A, selectively releases phosphate from serine 68, while alkali treatment releases phosphate from both sites. When analyzed as a substrate for six different protein kinases, only the Ca2+/phospholipid-dependent protein kinase modifies the matrix protein. The serine residues phosphorylated in vivo are identical to those phosphorylated in vitro by this protein kinase. The role of these phosphorylation events in viral production is discussed.     

Growth-promoting effects of acidic and basic fibroblast growth factor on rabbit articular chondrocytes aging in culture

Rabbit articular chondrocytes have a limited growth potential in vitro. After four passages in culture, chondrocytes have accomplished more than 50% of their life span. At this stage of culture, they are considered to be senescent-like, since a dramatic decrease in proliferative capacity and enhanced cell size and protein content are observed. These aged cells are, however, still able to respond to fibroblast growth factor (FGF). The addition of either acidic or basic FGF (10 ng/ml) to culture medium permitted an enhanced proliferation. The attenuation of FGF mitogenic activity during aging was not observed for both fractions. Moreover, when treated with acidic or basic FGF, aged chondrocytes had a smaller size and a lower protein content. The acidic FGF was less potent than the basic FGF in delaying the evolution of aged chondrocytes to senescence.     

Conserved residues of tumour necrosis factor and lymphotoxin constitute the framework of the trimeric structure

Four distinct areas of primary sequence conservation between known tumour necrosis factor and lymphotoxin polypeptides from various species can be recognized. When these amino acid sequences are highlighted in the three-dimensional structure, all are found in the same region, constituting the framework of the trimeric structure.     

Anaerobic dechlorination of 2,4-dichlorophenol in freshwater sediments in the presence of sulfate.

In the presence of added sulfate, 2,4-dichlorophenol and 4-chlorophenol were transformed stoichiometrically to 4-chlorophenol and phenol, respectively, in anaerobic freshwater lake sediments between 18 and 40 degrees C. The concomitantly occurring sulfate reduction reduced the initial sulfate concentration from 25 mM to about 6 to 8 mM and depressed methane formation.