Modulation of Coordinated Activity across Cortical Layers by Plasticity of Inhibitory Synapses

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Protonic and cationic changes during cyclical cation transport driven by electron transfer

A method is described for the subcellular fractionation of goldfish xanthophores. The procedure produces relatively pure fractions of caroteniod droplets, pterinosomes, cytosol and what appears to be plasma membrane. The presence of a distinct pattern of proteins is shown to be associated with the carotenoid droplets. Treatment of the xanthophores with ACTH affects the buoyant density of some carotenoid droplets and stimulates the phosphorylation of a polypeptide associated with the carotenoid droplets.     

Vitamin K epoxidase activity of rough and smooth microsomes from rat liver

The distribution of vitamin K epoxidase activity in rough and smooth microsomes has been studied and compared to the prothrombin precursor and vitamin K-dependent carboxylase activity. All three activities were high in rough microsomes as compared to the low levels found in smooth microsomes. The results are in agreement with the suggestion that there might be a linkage between the vitamin K-dependent carboxylation and epoxidation reaction in vivo.     

Selective increase in cytokeratin synthesis in cultured rat hepatocytes in response to hormonal stimulation

Addition of a combination of insulin, dexamethasone and EGF at seeding time to cultured rat hepatocytes in serum-free medium caused a selective increase in the biosynthesis of particular cytokeratin components. This increase was prominent during the first day in culture. No significant increases were detected in the absence of hormones or in the presence of either hormones added alone or in pairs, except in the case of insulin plus dexamethasone, which yielded an effect close to that obtained with the three factors. Interestingly, the latter condition also maintained a high level of albumin production over a 6-day period in culture.     

A bacterial clone carrying sequences coding for elongation factor EF-1 alpha from Artemia

A bacterial cDNA clone was identified carrying one third of the nucleotides coding for elongation factor EF-1 alpha from the brine shrimp Artemia. The sequence of codons corresponds with the known sequence of amino acids of EF-1 alpha in the region involved.     

Properties of SDS-polyacrylamide gels highly cross-linked with N,N'-diallyltartardiamide and the rapid isolation of macromolecules from the gel matrix.

Polyacrylamide gels cross-linked with N,N′-diallyltartardiamide (DATD) are, in contrast to gels cross-linked with N,N′-methylenebisacrylamide (Bis), readily solubilized by periodic acid (Anker, H. S., 1970, FEBS Lett.7, 293), thus permitting efficient analyses of electrophoretically separated, labeled biological material. The capacities of polyacrylamide gels, cross-linked with Bis and DATD, to serve as media for electrophoretic separation of proteins, were compared. As DATD-cross-linked gels were inferior to equimolar Bis-crosslinked gels with 5% cross-linking (C_Bis = 5%) by the criteria of more pronounced swelling, markedly softer gels and, less concentrated and bended protein zones on electrophoresis and subsequent staining, gels cross-linked with different percentage CDATD were examined. The water regain of DATD-cross-linked gels, the retardation coefficients, and free mobilities of different proteins in equimolar Bis- and DATD-cross-linked gels were determined. When the DATD concentration in gels was increased to C_DATD = 27%, gels assumed physical characteristics comparable to those cross-linked with Bis at C_Bis = 5%. We report further the rapid, facile isolation of protein bands out of the gel matrix cross-linked with DATD. However, the isolation procedure results in an irreversible loss of biological activity.     

Regulation of 5-phosphoribosyl-1-pyrophosphate synthesis in human fibroblasts by the concentration of inorganic phosphate

During the growth cycle of normal fibroblasts and of fibroblasts deficient in glucose-6-phosphate dehydrogenase activity, the concentration of 5-phosphoribosyl-1-pyrophosphate and of P_i, as well as the activity of 5-phosphoribosyl-1-pyrophosphate synthetase, decreased to stable values in confluent cultures. A high degree of correlation (0.89 and 0.91 for two normal and 0.69 for one glucose-6-phosphate dehydrogenase-deficient cell strain, respectively) was shown between intracellular P_i and 5-phosphoribosyl-1-pyrophosphate concentrations under varying culture and incubation conditions. 5-phosphoribosyl-1-pyrophosphate concentrations were elevated in normal fibroblasts incubated with methylene blue only if intracellular P_i levels were high. Neither methylene blue nor 6-aminonicotinamide, singly, affected intracellular P_i concentrations. However, when normal cells were pretreated with 6-aminonicotinamide and then with methylene blue, intracellular P_i decreased, 5-phosphoribosyl-1-pyrophosphate was depleted, and its rate of generation decreased. Under similar conditions, glucose-6-phosphate dehydrogenase-deficient fibroblasts maintained unaltered P_i levels, and 5-phosphoribosyl-1-pyrophosphate concentration and generation were slightly increased. The decrease in intracellular P_i in normal cells after the combined treatment was commensurate with an accumulation of 6-phosphogluconate, which did not take place in mutant cells. The changes in 5-phosphoribosyl-1-pyrophosphate synthesis, whether due to the stage of growth or various experimental manipulations, were always concordant with changes in intracellular P_i level. The regulatory role of P_i is consistent with the known enzymic properties of 5-phosphoribosyl-1-pyrophosphate synthetase.