The role of the tryptophyl residue in the hypotensive peptide xenopsin

The role of the Trp⁶ residue in the biological activity of the hypotensive peptide xenopsin (<Glu-Gly-Lys-Arg-Pro-Trp-Ile-Leu-OH) was investigated. This residue was satisfactorily reduced to 2,3-dihydro-Trp on treatment with excess pyridine-borane in trifluoroacetic acid without any detectable change in other parts of the molecule. The analogous peptide, (Lys², Gly³) xenopsin, was also reduced in a similar manner. Both reduction products were purified by gel filtration and characterized by UV absorption, amino acid composition, and structural analysis.The reduced peptides were assayed on the fundus strip of isolated rat stomach and were found to possess less than 1 percent of the activity of the original peptides. Although each of the reduced analogs had an indoline substituted for an indole in the tryptophyl residue, their biological activity was virtually lost. This suggests that the tryptophyl residue of xenopsin is crucial for its biological activity.     

Location of nuclear antigen(s) recognized by DSB389 MAb, a monoclonal antibody against desmin, observed by confocal laser scanning fluorescence microscopy

The location of antigen(s) of DSB389 MAb, a monoclonal antibody which was raised against an intermediate filament protein, desmin, was investigated in HeLa S3 cells by indirect immuno-electron microscopy and by confocal laser scanning fluorescence microscopy. At interphase, the antigen(s) locates mainly in the intra-nuclear space adjacent to chromatin and sometimes near the nuclear periphery. At mitosis, they locate at the periphery of the chromosomes -first at each chromosome, then around the mass of chromosomes. The antigen(s) are thought to be a component of one type of nuclear matrix which is present outside both chromatin and chromosomes and which has some structural role(s) in organizing them in the nucleus or in the nuclear region.     

Heterogeneous distribution of the precursor of type I and type III collagen and fibronectin in the rough endoplasmic reticulum of palatal mesenchymal cells of the mouse embryo cultured in ascorbate-depleted medium

Summary In order to examine the intracellular distribution of precursors of type I and type III collagen and fibronectin in the palatal mesenchymal (MEPM) cells of the mouse embryo cultured under ascorbate-deficient conditions, immuno-electron-microscopic studies were carried out by use of affinity purified antibodies for these proteins. MEPM cells were obtained from the palatal shelves of 14-day-old mouse fetuses and cultured for 3–7 days in medium, either with or without 50 ng/dish/day ascorbic acid. Results obtained were as follows: (1) Although the rough endoplasmic reticulum (rER) of MEPM cells cultured for 5 days in ascorbate-supplemented medium was flattened, that in cells cultured in ascorbate-deficient medium had a distended or vesicular appearance. (2) Vesicular or distended rER showed heterogeneous staining for both type I and type III collagen, namely, some parts of rER showed positive staining for both types of collagen, while others showed negative staining. (3) Both type I and type III collagen showed codistribution in the same vesicular rER. (4) Vesicular rER showed negative or very faint labelling for fibronectin. These results may suggest regional differences in the function of rER.     

Further studies on membrane transport with time delay

A theory of cell membrane transport with a time delay which predicts under certain conditions overshoot or oscillatory permeation (Ohshima and Kondo, Biophys. Chem. 33 (1989) 303), is extended with the introduction of a parameter expressing a fraction of solutes inside the cell interior that suffer time delay. It is found that criterion for oscillation depends strongly on this parameter. Results will also be presented for the case of an exponential-type distribution of the delay time.     

The effects of histamine and some related compounds on conditioned avoidance response in rats

When histamine (Hi) and other agonists were applied intraventricularly, Hi caused a dose-dependent inhibition of the avoidance response in rats; its ED50 was 3.60 micrograms. 1-methylHi, 1-methylimidazole acetic acid and imidazole acetic acid which are major metabolites of Hi produced no inhibitory effect even at 50 micrograms. H1-agonists (2-methylHi and 2-thiazolylethylamine) also depressed the avoidance response; their dose-response lines run parallel to that of Hi. The depressant effects of H2-agonists (4-methylHi and dimaprit) were relatively weak; their dose-response lines were not parallel to that of Hi. When antagonists were pretreated intravenously, Hi action was clearly antagonized by diphehydramine and pyrilamine, but not by cimetidine or ranitidine. Intraventricular injection of Hi mixed with cimetidine or ranitidine did not change the effect induced by Hi alone. The avoidance response was not affected by noradrenaline, dopamine or 5-hydroxytryptamine. Although acetylcholine (ACh) suppressed the avoidance response dose-dependently, its effect was much weaker than that of Hi. Pretreatment with cholinergic blocking drugs (atropine and scopolamine) antagonized ACh action but not Hi action. From these results, it is assumed that the inhibitory effect of Hi on the avoidance response is preferentially linked to the H1-receptor. After intraventricular application of 3H-Hi, the highest radioactivity was determined in the hypothalamus.     

Control of trophoblast cell differentiation: Lessons from the genetics of early pregnancy loss and trophoblast neoplasia

Trophoblast cell differentiation is crucial to the morphogenesis of the placenta and thus the establishment of pregnancy and the growth and development of the embryo/fetus. In the present review, we discuss current evidence for the existence of regulatory genes crucial to trophoblast cell differentiation and placental morphogenesis. The elucidation of regulatory pathways controlling normal differentiation of trophoblast cells will facilitate the identification of sensitive junctures in the regulatory pathways leading to various developmental disorders, including those associated with the initiation of pregnancy, fetal growth retardation and gestational trophoblast disease.     

Occurrence and induction of spermidine-N1-acetyltransferase in Escherichia coli

Spermidine acetylase activity was detected in extracts prepared from $\text{Escherichia coli}$ and there was a marked increase in activity over the early period of growth. This increase reached a maximum 3 h after inoculation and was followed by an increase in ornithine decarboxylase activity. The acetylase was also able to use spermine as a substrate, but not putrescine. With spermidine and acetyl-CoA as substrate, the product formed was exclusively N¹-acetyl-spermidine. This is the first evidence for the occurrence in bacteria of spermidine-N¹-acetyltransferase, an enzyme which has previously been described in mammalian cells. These results suggest that acetylation of spermidine may be involved in the growth of $\text{Escherichia coli}$ and in the regulation of its polyamine content.     

Chemical modification of pig liver initiation factor eIF-2 with N-ethylmaleimide. Amino acid sequences around the N-ethylmaleimide-reactive sulfhydryl groups and the effect of GDP on the modification

The activity of eukaryotic initiation factor eIF-2 as to the formation of the ternary complex, eIF-2 GTP Met-tRNA(f), is inhibited by N-ethylmaleimide. Our preparation of pig liver eIF-2 contained alpha and gamma subunits and was inhibited by more than 90% by N-ethylmaleimide. Using our eIF-2, we determined the sequences around the N-ethylmaleimide-reactive sulfhydryl groups, studied the effect of GDP on the sulfhydryl modification and that of NEM on the [3H]GDP binding, and examined the protective effect of GTP against the inhibition of ternary complex formation by N-ethylmaleimide. Both subunits of native eIF-2 contained [14C]N-ethylmaleimide-reactive sulfhydryl groups. One N-ethylmaleimide-reactive sulfhydryl group was in the alpha subunit and 4 were in the gamma subunit. The sequence of the peptide of the alpha subunit was determined to be: Ala-Gly-Leu-Asn-Cys-Ser-Thr-Glu-Thr-Met-Pro-Ile. Two of the four [14C]N-ethylmaleimide-reactive sulfhydryl groups in the gamma subunit were highly reactive, their sequences being: Ile-Val-Leu-Thr-Asn-Pro-Val-Cys-Thr-Glu-Val-Gly-Glu-Lys (gamma 1); Ser-Cys-Gly-Ser-Ser-Thr-Pro-Asp-Glu-Phe-Pro-Thr-Asp-Ile-Pro-Gly-Thr-Lys (gamma 3a). Peptide gamma 3a contained the consensus sequence element (AspXaaXaaGly) of GTP-binding proteins. With preincubation of eIF-2 with GDP, the incorporation of [14C]N-ethylmaleimide into the gamma subunit was reduced to 40% of the control level, but the 14C-incorporation into the alpha subunit did not change.(ABSTRACT TRUNCATED AT 250 WORDS)