Echinomycin and distamycin induce rotation of nucleosome core DNA.

When nucleosome cores reconstituted from chicken erythrocyte histones and a 160 bp DNA molecule are exposed to echinomycin, a bis-intercalating antitumour antibiotic, the DNA appears to rotate with respect to the histone octamer by about half a turn. New bands appear in patterns of DNAase I digestion at positions approximately mid-way between those characteristic of control core samples, while the control pattern is largely suppressed. Similar (but not identical) changes are produced when nucleosome cores are exposed to distamycin, a non-intercalating DNA-binding antibiotic. The effects of both ligands can be explained in terms of a change in rotational orientation of the core DNA, so as to place antibiotic binding sites on the inward-facing (concave) surface of the DNA supercoil. Presumably this serves to optimise non-bonded contacts with the polynucleotide backbone. These results establish that the positioning of DNA about the histone octamer is not absolutely determined by its nucleotide sequence, but may be modified by the binding of such relatively small molecules as antibiotics.     

Induction of heavy metal binding groups by dexamethasone and Zn in cultured Chinese hamster ovary cells

Cd binding capacity and pulse polarography were used to study the inducibility of sulfhydryl groups in cultured Chinese hamster ovary cells (wild type and a Cd-resistant mutant) in response to dexamethasone (dex) and Zn. Evidence is presented that both the wild type and the mutant responded to dex and Zn treatment by induction of sulfhydryl groups. In wild type for Zn and dex as well as in the mutant for dex, this induction seems to be in the form of sulfhydryls attached to particulate or membrane fractions in the cells. For Zn in the Cd-resistant mutant the induction was in the form of metallothionein.     

Effect of ethionine on synthesis and methylation of ribosomal ribonucleic acid in regenerating rat liver

Ethionine, a hepatocarcinogen, was administered into rats 24 h before partial hepatectomy and immediately thereafter. Hepatic precursor ribosomal RNA (pre-rRNA) obtained 20 h after the operation of rats injected with ethionine and adenine resulted in methyl deficiency as judged by the incorporation of [3H]methyl group of S-adenosylmethionine into nuclear rRNA by partially purified rRNA methylase. The ethionine and adenine treatment causes methyl deficiency of nuclear rRNA at 2'-hydroxyribose sites of cytidine and uridine, but not at base sites. Although the ethionine and adenine treatment produced no significant change in total hepatic RNA synthesis in vivo assayed by the incorporation of labeled orotate, a one-third increase in nuclear rRNA synthesis as well as a one-third decrease in microsomal rRNA synthesis was found under the treatment. These results suggest that the undermethylation at 2'-hydroxyribose of pre-rRNA in liver nucleus, which is caused by ethionine and adenine administration into rats, causes an inhibition of the processing of nuclear pre-rRNA to cytoplasmic rRNA.     

Pinocytosis and intracellular degradation of exogenous protein: modulation by amino acids

Intracellular degradation of exogenous (serum) proteins provides a source of amino acids for cellular protein synthesis. Pinocytosis serves as the mechanism for delivering exogenous protein to the lysosomes, the major site of intracellular degradation of exogenous protein. To determine whether the availability of extracellular free amino acids altered pinocytic function, we incubated monolayers of pulmonary alveolar macrophages with the fluid-phase marker, [14C]sucrose, and we dissected the pinocytic process by kinetic analysis. Additionally, intracellular degradation of endogenous and exogenous protein was monitored by measuring phenylalanine released from the cell monolayers in the presence of cycloheximide. Results revealed that in response to a subphysiological level of essential amino acids or to amino acid deprivation, (a) the rate of fluid-phase pinocytosis increased in such a manner as to preferentially increase both delivery to and size of an intracellular compartment believed to be the lysosomes, (b) the degradation of exogenously supplied albumin increased, and (c) the fraction of phenylalanine derived from degradation of exogenous albumin and reutilized for de novo protein synthesis increased. Thus, modulation of the pinosome-lysosome pathway may represent a homeostatic mechanism sensitive to the availability of extracellular free amino acids.     

Variations in problem conceptualizations and intended solutions among Hong Kong students

Cognitive schema were used to explain health and illness behaviors among Chinese students. University students in Hong Kong were asked to attribute causes and suggest solutions to five health/mental health problems: Weakness/Fatigue, Tension/ Anxiety, Sleep Difficulty, Hollow/Emptiness, and Headache. The patterns of endorsement on the causal and solution categories used for the five problems were compared using a new asymptotic chi-squared test. The response patterns were found to be significantly different across the five problems. Each problem was attributed to multiple causes including psychological, social, situational, somatic, and existential factors. The intended solutions were often related to the nature of the causal attributions especially when the problems were mild. In lay help-seeking, the Hong Kong students would attempt a variety of self-help measures. However, for professional consultation, the medical doctor would be the primary care professional the students would turn to for most of the problems except in the case of Hollow/Emptiness.     

Raman spectroscopic and X-ray diffraction studies of the effect of temperature and Ca2+ on phosphatidylethanolamine dispersions

Raman spectroscopy and X-ray diffraction are used to study the effect of heat and Ca²⁺ on dimyristoylphosphatidylethanolamine dispersions. Unlike phosphatidylcholine dispersions, dimyristoylphosphatidylethanolamine bilayers (at pH 8) require heating above T_m in order for hydration to occur and apparently bind Ca²⁺ at very low levels. These results are related to models for membrane fusion.     

Resolution of myocardial phospholipase C into several forms with distinct properties.

Phospholipase C activity capable of hydrolysing phosphatidylinositol in bovine heart was resolved into four forms (I-IV) by ion-exchange chromatography. Some of these forms could only be detected if the assay was performed at acidic pH (I and IV) or in the presence of deoxycholate (II). Gel-filtration chromatography indicated that the four forms had different molecular weights in the range 40000-120000. I, II and III all had pH optima in the range 4.5-5.5. However, the major form (III) also had substantial activity at pH 7.0 and above. The activities of I, II and III at pH 7.0 were stimulated by deoxycholate; this effect was most marked with I and II, which had very low activity at this pH. All forms of the enzyme were inhibited by EGTA and required 2-5 mM-CaCl2 for maximal activity. When the fractions eluted from the ion-exchange and gel-filtration columns were assayed with polyphosphoinositides as substrates there was a close correspondence to the elution profile obtained with phosphatidylinositol as substrate; there was no evidence for the existence in heart of phospholipase C activities specific for individual phosphoinositides.     

Effects of insulin in vitro on protein turnover in rat epitrochlearis muscle.

The hexapeptide Arg-Asn-Gly-epoxyethylglycine-Ala-Val-OMe specifically inactivates membrane-bound N-glycosyltransferases. The specificity is demonstrated by the inability of peptides containing 2,3-epoxypropyl-, allyl- and vinyl-glycine in the epoxyethylglycine position to function as inhibitors. The inhibition is concentration-dependent and follows first-order kinetics, but requires disruption of the membrane vesicles by detergents to achieve accessibility to the transferase. The enzyme can be protected partially against inactivation by the addition of the acceptor peptide Arg-Asn-Gly-Thr-Ala-Val-OMe, pointing to an active-site-directed reaction. Exhaustion of the endogenous pool of glycosyl donor molecules by preincubation of the membrane vesicles with the acceptor peptide before inhibitor application is accompanied by an additional decrease in the inhibition rate. This suggests that inactivation occurs only under conditions where glycosyl transfer is catalysed. A mechanism of inactivation is proposed in which the transferase catalyses its own inactivation by a kind of 'suicide' mechanism.     

Relation of Catalase to Substrate Utilization by Mycoplasma pneumoniae

No catalase activity was detected in four strains of glucose-grown Mycoplasma pneumoniae at any time during the replication of the organism. Exogenous catalase dramatically increased the O(2) uptake with glycerol, presumably by releasing inhibition caused by hydrogen peroxide. The effect of added catalase on the O(2) uptake of washed organisms with glucose as substrate was moderate and variable in degree. The production of hydrogen peroxide was demonstrated by the quantitative enzymatic assay for inorganic peroxide and by the fact that added pyruvate, which is non-enzymatically oxidized by H(2)O(2) to acetic acid and CO(2) could mimic the action of catalase.