24-hour variation in content and release of hypothalamic neuropeptides in the rat

The tissue content of up to eight neuropeptides, viz bombesin (BOM), cholecystokinin (CCK-8), neurotensin (NT), neuropeptide Y (NPY), peptide histidine isoleucine amide (PHI), somatostatin (SRIF), substance P (SP) and vasoactive intestinal polypeptide (VIP), in rat hypothalami removed at various times of the day, was measured using specific radioimmunoassays. There was significant variation in the content of BOM, CCK-8, NT, PHI, SP and VIP across a 24-h period. The levels of BOM, CCK-8 and NT were lowest around the onset of darkness (1900 h) and rose throughout the night to reach a peak around the time of lights on. Hypothalamic content of all eight peptides fell between 0700 h and 1300 h by an average of 45 +/- 4%. Basal release of these peptides, as well as that in the presence of 48 mM potassium (K+), was measured from hypothalami removed between 0700 and 1900 h and incubated in vitro in a CSF-like medium. Basal secretion of NT significantly increased, whilst that of CCK-8 significantly decreased over the same period. There was no significant change in the basal release of the other neuropeptides. The release in the presence of 48 mM K+ of SP decreased significantly during the day, whilst that of VIP significantly increased. There was also a significant change in the stimulated release of BOM, levels falling during the morning and rising again at 1900 h. 48 mM K+ caused a significant increase in the release of SRIF and SP at all times tested. Whilst 48 mM K+ induced a significantly higher release of CCK-8 and NT in the morning, this stimulus was ineffective in the evening. The contrary was true in the case of BOM, NPY and VIP, where a significant stimulation was induced only at 1900 h. The possible implications of these findings are discussed.     

Modulation of locomotor activity by substance P in rats

The effects of intraperitoneally or intracerebrally (DA A-10 area) administered substance P (SP) on locomotor activity of rats were studied in an exact 12-h light/12-h dark cycle changing from dark to light at 6 a.m. SP was administered either at 11 a.m. (light phase, minimal locomotor activity) or at 7 p.m. (dark phase, maximal locomotor activity). The effects of 12.5 micrograms/kg SP intracerebral and 125 micrograms/kg SP intraperitoneal were very similar. In the light phase SP produces excitation but inhibition of locomotion in darkness. Hence, the effect of SP depends on the internal mechanisms controlling motor activity and tends to level off the spontaneous circadian oscillation. We found a long lasting SP effect during both the light and dark period. The present experiments led us to the conclusion that SP has a levelling effect on locomotor activity. Probably this effect might be explained as SP's action on the dopaminergic pathway or dopamine metabolism, because the dopamine content in neurons also has a circadian rhythm.     

Thiolated nucleotides in yeast transfer RNA

By culturing Saccharomyces cerevisiae in growth medium containing Mg³⁵SO₄, we have determined the extent and variation of tRNA thiolation in this yeast. We find that 5-methoxycarbonylmethyl-2-thiouridine (mcm⁵s²U)¹ is the major, if not only, thiolated derivative in S. cerevisiae tRNA. In addition, a comparison of the chromatographic mobility of mcm⁵s²Up on cellulose thin layers with those reported for unknown uridine derivatives found in purified yeast tRNA digests, leads to the conclusion that at least two of these tRNAs contain this modification.     

Complex organization of a cryptic satellite DNA in the genome of the marine invertebrate Rapana thomasiana Grosse (Gastropoda)

Isopicnic centrifugation in Cs₂SO₄-Ag⁺ gradients at pH 7.0 reveals that the genome of the marine snail Rapana thomasiana Grosse (Gastropoda) contains an AT-rich satellite fraction comprising 5% of the DNA. Restriction enzyme analysis shows that the satellite DNA is composed of a number of related subsets arranged in tandem arrays. They have evolved from the segmental amplification of an 1460 bp long monomer unit with a complex inner organization. Most probably, the present basic repeat originates from an ancestral 400–500 bp long sequence in which some insertions and/or deletions have occurred.     

Requirements for antiribosomal activity of pokeweed antiviral protein

It has been known for some time that pokeweed antiviral protein acts by enzymatically inhibiting protein synthesis on eucaryotic ribosome systems. The site of this action is known to be the ribosome itself. In this paper we show that the pokeweed antiviral protein reaction against ribosomes is a strong function of salt concentrations, where 160 mM K⁺ and 3 mM Mg²⁺ retards the reaction, while 20 mM K⁺ and 2 mM Mg²⁺ allows maximum reaction rate. It is also shown, however, that an unidentified protein in the postribosomal supernatant solution, together with ATP, allows the ribosome to be attacked even in the presence of high salt. Kinetic analysis of the antiviral protein reaction has been carried out under both sets of conditions, and reveals that the turnover number for the enzyme is about 300–400 mol/mol per min. in each case. The K_m for ribosomes is 1 μM in the presence of low salt and 0.2 μM at higher salt in the presence of postribosomal supernatant factors plus ATP. The antiviral protein reaction is also shown to be pH dependent and is controlled by a residue with pK_a value of approx. 7.0, apparently a histidine. Stoichiometric reaction of the enzyme with iodoacetamide results in a significant loss of antiribosomal activity.     

Secondary structure features of ribosomal RNA species within intact ribosomal subunits and efficiency of RNA-protein interactions in thermoacidophilic (Caldariella acidophila,Bacillus acidocaldarius) and mesophilic (Escherichia coli) bacteria

Ribosomal subunits of Caldariella acidophila (max.growth temp., 90°C) have been compared to subunits of Bacillus acidocaldarius (max. growth temp., 70°C) and Escherichia coli (max. growth temp., 47°C) with respect to (a) bihelical content of rRNA; (b) G·C content of bihelical domains and (c) tightness of rRNA-protein interactions. The principal results are as follows. 1. Subunits of C. acidophila ribosomes (T_m = 90–93°C) exhibit considerable thermal tolerance over their B. acidocaldarius (T_m = 77°C) and E. coli counterparts (T_m = 72°C). 2. Based on the ‘melting’ hyperchromicities of the intact ribosomal subunits a 51–55% fraction of the nucleotides appears to participate in hydrogen-bonded base pairing regardless of ribosome source, whereas a larger fraction, 67–70%, appears to be involved in hydrogen bonding in the naked rRNA species. 3. The G·C content of bihelical domains of both free and ribosome-bound rRNA increases with increasing thermophily; based on hyperchromicity dispersion spectra of intact subunits and free rRNA, the bihelical parts of C. acidophila rRNA are estimated to contain 63–64% G·C, compared to 58.5% G·C for B. acidocaldarius and 55% G·C for E. coli. 4. The increment in ribosome T_m values with increasing thermophily is greater than the increase in T_m for the free rRNA, indicating that within ribosomes bihelical domains of the thermophile rRNA species are stabilized more efficiently than their mesophile counterparts by proteins or/ and other component(s). 5. The efficiency of the rRNA-protein interactions in the mesophile and thermophile ribosomes has been probed by comparing the releases, with LiCl-urea, of the rRNA species from the corresponding ribosomal subunits stuck to a Celite column through their protein moiety; it has been established that the release of C. acidophila rRNA from the Celite-bound ribosomes occurs at salt-urea concentrations about 4-fold higher than those required to release rRNA from Celite-bound E. coli ribosomes. 6. Compared to E. coli, the C. acidophila 50 and 30 S ribosomal subunits are considerably less susceptible to treatment designed to promote ribosome unfolding through depletion of magnesium ions.     

Ligation of highly modified bacteriophage DNA

After digestion by TaqI or nicking by DNAase I, five highly modified bacteriophage DNAs were tested as substrates for T4 DNA ligase. The DNAs used were from phages T4, XP12, PBS1, SP82, and SP15, which contain as a major base either glucosylated 5-hydroxymethylcytosine, 5-methylcytosine, uracil, 5-hydroxymethyluracil, or phosphoglucuronated, glucosylated 5-(4′,5′-dihydroxypentyl)uracil, respectively. The relative ability of cohesive-ended TaqI fragments of these DNAs and of normal, λ DNA to be ligated was as follows: $\text{λ}\text{DNA}\text{=}\text{XP}\text{12}\text{DNA}\text{>}\text{SP}\text{82}\text{DNA}\text{?}\text{nonglucosylated}\text{T}\text{4}\text{DNA}\text{>}\text{T}\text{4}\text{DNA}\text{=}\text{PBS}\text{1}\text{DNA}\text{?}\text{SP}\text{15}\text{DNA}$. TaqI-T4 DNA fragments were also inefficiently ligated by Escherichia coli DNA ligase. However, annealing-independent ligation of DNAase I-nicked T4, PBS1, and λ DNAs was equally efficient. We conclude that the poor ligation of TaqI fragments of T4 and PBS1 DNAs was due to the hydroxymethylation (and glucosylation) of cytosine residues at T4's cohesive ends and the substitution of uracil residues for thymine residues adjacent to PBS1's cohesive ends destabilizing the annealing of the restriction fragments. Only SP15 DNA with its negatively charged, modified base was unable to serve as a substrate for T4 DNA ligase in an annealing-independent reaction; therefore, its modification directly interfered with enzyme binding or catalysis.     

Effect of hemolysate on calcium inhibition of the (Na+ + K+)-ATPase of human red blood cells

The sensitivity of the (Na+ + K+)-ATPase in human red cell membranes to inhibition by Ca2+ is markedly increased by the addition of diluted cytoplasm from hemolyzed human red blood cells. The concentration of Ca2+ causing 50% inhibition of the (Na+ + K+)-ATPase is shifted from greater than 50 microM free Ca2+ in the absence of hemolysate to less than 10 microM free Ca2+ when hemolysate diluted 1:60 compared to in vivo concentrations is added to the assay mixture. Boiling the hemolysate destroys its ability to increase the sensitivity of the (Na+ + K+)-ATPase to Ca2+. Proteins extracted from the membrane in the presence of EDTA and concentrated on an Amicon PM 30 membrane increased the sensitivity of the (Na+ + K+)-ATPase to Ca2+ in a dose-dependent fashion, causing over 80% inhibition of the (Na+ + K+)-ATPase at 10 microM free Ca2+ at the highest concentration of the extract tested. The active factor in this membrane extract is Ca2+-dependent, because it had no effect on the (Na+ + K+)-ATPase in the absence of Ca2+. Trypsin digestion prior to the assay destroyed the ability of this protein extract to increase the sensitivity of the (Na+ + K+)-ATPase to Ca2+.     

Protective effects of differentiation inducers on natural killer sensitivity of K 562 cells: Analysis at a single-cell level

K 562 cells induced to differentiate by sodium butyrate (SB) or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) were studied for their capacities to be bound and killed by large granular lymphocytes (LGL) in a single-cell cytotoxicity assay in agarose. After SB treatment, K 562 cells were less efficient in binding to LGL, whereas the frequency of killer cells among bound LGL was unaffected. When TPA was used to induce K 562 differentiation, the binding of LGL to their target and the lytic efficiency of the bound LGL were both diminished when compared to control K 562 cells. It has been demonstrated that the expression of structures involved in the binding of natural killer (NK) effectors to their targets could be correlated with the target-differentiation stage. It is shown that phorbol-ester treatment can also affect NK target structures involved in the killing step.     

Characterization of an immune suppressor from transformed human trophoblastic JEG-3 cells

Cultured human choriocarcinoma JEG-3 cells secrete an immunosuppressor that inhibits lymphocyte proliferation stimulated by either an antigen or a mitogen. In this study, the immunosuppressive factor was characterized by three methods: ion-exchange and exclusion chromatography, partition in organic solvents, and thin-layer chromatography on silicic acid. This JEG-3 cell factor appeared to be a protein complex of about 150,000–200,000 Da that contained an immunologically active polar lipid. The structural and functional characteristics of JEG-3 cell immunosuppressor are similar if not identical to those of SIF, a suppressor lymphokine derived from T cells. These secretions from transformed trophoblastic cells may correspond to normal placental products or represent a function of malignant cells.