Polymer concentration dependence of the helix to random coil transition of a charged polypeptide in aqueous salt solution.

The helix to coil transition of poly(L-glutamic acid) was investigated in 0.05 and 0.005 M aqueous potassium chloride solutions by use of potentiometric titration and circular dichroism measurement. Polymer concentration dependence of the transition was observed in the range from 0.006 to 0.04 monomol/e in 0.005 M KG1 solution. The polymer concentration dependence can be interpreted by current theories of the transition of charged polypeptides and of titration curves of linear weak polyelectrolytes taking the effect of polymer concentration into consideration.     

Selective expression of cell type specific cell-cell adhesion molecules in mouse hybrid cells

Abstract. Ca²⁺-dependent cell-cell adhesion systems (CDS) are present in a variety of cells which can be grouped into at least two qualitatively different types, the teratocarcinoma type (t-CDS) and the fibroblast type (f-CDS), where different classes of adhesion molecules operate, respectively. In order to study the regulatory mechanisms of expression of different CDS types, we made cell hybrids between teratocarcinoma OTF9 cells (t-CDS) and fibroblast L cells (f-CDS), and between OTF9 cells (t-CDS) and hepatoma MH cells (no CDS). We thus examined which type of CDS is expressed in hybrid clones using a probe, an antibody that recognizes t-CDS selectively. We isolated many hybrid clones with different phenotypes, all displaying CDS activity, and found that CDS functioning in each clone was either t-CDS or another type(s) of CDS. There were no clones in which both t-CDS and another type(s) of CDS are active. We therefore suggested that the expression or function of t-CDS and other types of CDS is mutually exclusive within a single cell.     

Isolation of protoplasts from somatic embryos of carrot

Protoplasts were isolated enzymatically from synchronously induced globular somatic embryos from a carrot suspension culture. Among the macerating enzymes tested, Driselase was the most effective for release of protoplasts from embryos. A higher medium osmolarity was required for the isolation of protoplasts from embryos than from undifferentiated cells. Protoplasts from embryos were smaller than protoplasts from undifferentiated cells. On step gradients of Ficoll, protoplasts from embryos gave one major band. Protoplasts from undifferentiated cells gave two major bands, one lighter and the other heavier than the protoplasts from embryos.     

Permanganate oxidation of nucleic acid components: a reinvestigation.

KMnO4 consumption in solution by nucleoside added at an excess was measured to explore any possible oxidative interactions between these molecules. Thymidine, 5-methyldeoxycytidine and deoxycytidine rapidly decomposed KMnO4 with the pseudo-first-order kinetics (thymidine greater than 5-methyl-deoxycytidine greater than deoxycytidine), while deoxyguanosine showed only a very slow consumption and deoxyadenosine did not decompose KMnO4 at all under the conditions employed (0.16 mM KMnO4, 0.80 mM nucleoside, at 27 degrees C and pH 4.3, 7.4 and 8.6, up to 60 min). UV absorption spectra of KMnO4-treated nucleosides also indicated modification of the pyrimidine nucleosides but not of the purine nucleosides. These results are consistent with the original report of Hayatsu and Ukita published in 1967 on the KMnO4 oxidation of nucleosides, and provide difficulty in understanding the mechanism of recently reported formation of 8-hydroxypurines on treatment of DNA with KMnO4.     

Different profiles of induced cotton effects of human and bovine lactoferrin by cibacron blue F3GA binding.

1. The properties of complex formation of lactoferrin with Cibacron Blue F3GA dye have been studied by circular dichroic spectral analyses. The Cotton effects were induced by the interaction of lactoferrin with the dye and occurred in the wavelength range from 300 to 450 nm. 2. The patterns of changes in circular dichroic spectra of lactoferrin induced by the dye were different in bovine and human lactoferrin. 3. Iron ions bound to lactoferrin affected the profiles of induced Cotton effects in human lactoferrin but not in bovine lactoferrin. 4. While the dye bound co-operatively to human apo-lactoferrin, such co-operativeness was not observed in iron-saturated human lactoferrin.     

Clonal growth and mesenchymal differentiation of PCC3/A/1 teratocarcinoma cells in serum-free medium

Clonal culture of PCC3/A/1 teratocarcinoma stem cells in serum-free medium has been achieved with feeder layers. Under this culture condition, stem cells effectively differentiated into various types of somatic cells, in particular chondrocytes and adipocytes. Myotubes and neuron-like cells also appeared, but infrequently. Embryonic endoderm cells were rarely observed. There appeared to be two stages in the differentiation process; In the early stage, only fibroblastic cells were found with the undifferentiated stem cells. In the later stage, chondrocytes and adipocytes predominated. Chondro-adipocyte differentiation occurred only after fibroblastic cell differentiation, an indication that fibroblastic cells may have an important function in chondro-adipocyte differentiation. Thus, the serum-free culture of PCC3/A/1 cells provides a suitable system with which to study the cell lineages and regulatory mechanisms of chondro-adipocyte differentiation.     

Radiobromine labeled norcholesterol analogs. Synthesis and tissue distribution study in rats of bromine-82 labeled 6β-bromomethyl-19- norcholest-5(10)-en-3β-ol

6β-Bromomethyl-19-norcholest-5(10)-en-3β-o1 (NCL-6-Br) was synthesized directly from cholest-5-ene-3β,19-diol 19-toluene-psulfonate $\text{via}$ homoallylic rearrangement with ammonium bromide or sodium bromide in acetonitrile. This method was applied to the radiolabeling of NCL-6-Br with bromine-82. Tissue distribution of bromine-82 labeled NCL-6-Br (NCL-6-Br-82) in rats was determined. The mean percent dose per gram uptake in adrenal at 24 and 120 h was 98 and 80 %/gm, respectively, which indicated a higher adrenal uptake as compared to iodine-131 labeled 19-iodocholest-5-en-3β-o1 (CL-19-I-131), but was at a lower level than that achieved with iodine-131 labeled 6β-iodomethy 119-norcholest-S(10)-en-3β-o1 (NCL-6-I-131). The ratio of radioactivity in the adrenal-to-liver concentration was also lower than that of CL-19-I-131 or NCL-6-I 131.     

Studies on the production of indole-3-acetic acid with auxin-heterotrophic mutants derived from cultured crown gall cells

Mutants in the indole-3-acetic acid metabolism derived fromcultured crown gall cells were tested to see whether they couldutilize any one of eight indolic compounds in place of indole-3-aceticacid. Two auxin-heterotrophic mutant cell lines could not utilizeindolepyruvic acid, but growth recovered when there was a supplementof indole-3-acetic acid. Indoleacetonitril and indoleacetaldoximeinhibited the growth of mutant cell lines and their parentalcrown gall cells. Cultured crown gall cells may have synthesizedindole-3-acetic acid from tryptophan via indolepyruvic acidand indole-acetaldehyde, and also may be able to produce indole-3-aceticacid from tryptophan via tryptamine (Received May 6, 1980; )     

The Activin A-Dependent Proliferation of PCC3/A/1 Embryonal Carcinoma Cells in Serum-Free Medium

Examination of the growth requirements of murine embryonal carcinoma cells (EC cells) or embryonic stem cells (ES cells) in serum-free medium revealed that PCC3 EC cells required activin A to grow and/or survive in such medium. In the absence of activin A, PCC3 cells began to disintegrate within 3 days under any serum-free conditions examined. P19 and AT805 EC cells grew even in serum-free medium without activin A but their growth rates were slightly facilitated by its addition. F9 EC cells also grew in the medium without activin A and its addition somewhat inhibited their growth rate. Three independently isolated ES cell lines and feeder-dependent PSA-1 EC cells also grew in serum-free medium without activin A if leukemia inhibitory factor (LIF) was supplemented. The addition of activin A had little effect on their growth rates. These findings suggest that PCC3 EC cells are a sort of nutritional mutant requiring activin A, thus making them useful in stidies on the growth regulatory mechanisms of EC/ES cells and/or the action of activin on EC/ES cells.