Biochemistry and ultrastructure of iridescent virus type 29

Physical and chemical parameters of iridescent virus type 29, isolated from the mealworm, Tenebrio molitor, have been analyzed. The icosahedral capsid is 130–135 nm in diameter and is surrounded by a fringe of coarse filaments. The virus has a buoyant density in CsCl of 1.31 g cm^?3 and contains 20 to 25 structural proteins as analyzed by isoelectric focusing and SDS-polyacrylamide gel electrophoresis. The DNA has a buoyant density in CsCl of 1.6874 g cm^?3 indicating a G + C content of approximately 28%. The lipid components of this virus differ from those of the host cell; the virus contains about 80% cardiolipin and 20% phosphatidyl choline.     

Reduction in Brain Glucose Utilization Rate after Tryptophol (3-Indole Ethanol) Treatment

Abstract: 3-Indole ethanol has been recently identified as the hypnotic agent in trypanosomal sleeping sickness, and because it is formed in vivo after ethanol or disulfiram treatment, it is also associated with the study of alcoholism. When administered intraperitoneally to rats (250 mg/kg) tryptophol induced a sleep-like state that lasted less than an hour (no righting reflex was apparent 2 min after injection, but it returned at 11 min in bovine serum albumin solution, and 47 min in 40% ethanol solution). In ethanol solutions, tryptophol reduced brain cortical glucose utilization by 55% to the basal brain metabolic rate, and this effect lasted less than 1 h. Synergistic effects of tryptophol and ethanol were suggested by the observation that in albumin solution, tryptophol reduced brain glucose utilization by 35%, but a normal rate was not observed until 2 h postinjection.     

Effectors of lipoprotein lipase secretion from isolated cardiac muscle cells incubated in vitro

Cycloheximide, colchicine, tunicamycin, glucagon, dibutyryl-3′–5′-cyclic AMP, dexamethasone and hydrocortisone had no effect on the lipoprotein lipase activity associated with rat cardiac muscle cells incubated $\text{in vitro}$. However, the steroid hormones and inhibitors affected profoundly the appearance of extracellular enzyme during the incubations. The pattern of effects, was consistent with lipoprotein lipase being a normal secretory product of heart muscle cells.     

Spinal analgesia: Comparison of the mu agonist morphine and the kappa agonist ethylketazocine

The sites of analgesic action of the mu agonist morphine and the purported kappa agonist ethylketazocine (EKC) were compared. Using local drug injections and parenteral administration of drugs to spinalized rats, our data support a predominantly spinal site of action for EKC and a major supraspinal action for morphine in antinociceptive tests. This spinal analgesic action of EKC was dose dependent and naloxone reversible indicating opiate receptor involvement. The possibility that EKC activates a spinal kappa receptor population is under further study.     

Age-related motor and catecholomine alterations in mice on levodopa supplemented diet

Old mice reared on regular diet show reduced motor activity, decreased basal adenylate cyclase, and increased MAO activities compared to adults. Brain DDC and COMT activities, DA, NE levels and DA-stimulated adenylate cyclase remained unchanged. By contrast, mice fed levodopa for life did not develop decreased motor activity with aging, lived about 50% longer, had slightly elevated whole brain DA and NE levels and failed to develop the expected rise in MAO activity with aging. Levodopa did not alter the number of dopaminergic and muscarinic cholinergic receptors or the adenylate cyclase activity in the striatum during aging. On levodopa, hepatic and renal DA, dopa, and HVA increased but the latter two returned to basal levels by mid life. In liver, DDC was unchanged but MAO tended to be higher in levodopa-fed mice. Thus, motor impairment is an age-related phenomenon in mice associated with selective alterations in brain dopaminergic systems, which may be prevented by dietary levodopa. Extracerebral tissues, through possibly adaptive metabolic mechanisms, play a significant role in regulating brain catecholamines during chronic administration of large doses of levodopa.     

Cell division cycle mutants altered in DNA replication and mitosis in the fission yeast Schizosaccharomyces pombe

Summary A total of 59 new temperature sensitive cdc mutants are described which grow normally at 25°C but become blocked at DNA replication or mitosis when incubated at 36°C. Thirtynine of the mutants are altered in cdc genes which have been identified previously. The remaining 20 mutants define 10 new cdc genes. These have been characterised physiologically, and 6 of the genes (cdc 17, 20, 21, 22, 23, 24) were found to be required for DNA replication, 2 for mitosis (cdc 27, 28), and 2 (cdc 18, 19), could not be unambigously assigned to either DNA replication or mitosis but were definitely required for one or the other.Three genes, the previously identified cdc 10, and cdc 20, 22 are likely to be required for the initiation of DNA replication. Mutants in two genes, cdc 17, 24 undergo bulk DNA synthesis at 36°C, but this DNA is defective. In the case of cdc 17 the defect is in the ligation of Okazaki fragments. cdc 23 is required for bulk DNA synthesis, whilst cdc 21 may possibly be required for the initiation of a particular sub-set of replicons.A previously isolated mutant cdc 13.117 is also further described. This mutant becomes blocked in the middle of mitosis with apparently condensed chromosomes.     

Comparison between mutagenesis in normal and transformed syrian hamster fibroblasts: Difference in the temporal order of HPRT gene replication

A highly tumorigenic subdiploid cell line, BP6T, derived in our laboratory from Syrian hamster embryo (SHE) cells, is amenable to studies of somatic mutation in vitro. Cellular and biochemical characterization of clonally derived BP6T cells resistant to 6-thioguanine (TG^r) or ouabain (Oua^r) demonstrated these mutants to be similar qualitatively to mutants of SHE cells characterized previously (Barrett et al., 1978). BP6T TG^r mutants resistant to 6-thioguanine are cross-resistant to 8-azaguanine, lack HPRT activity, exhibit a low frequency of reversion and arise spontaneously at a rate of 5 × 10⁻⁷ mutants per cell per generation. BP6T Oua^r mutants were shown to be highly resistant to ouabain-mediated inhibition of ⁸⁶Rb influx, indicating an alteration in the Na⁺/K⁺ ATPase. These studies on the BP6T cell line provide the experimental basis for a comparative study of the mutagenic responses of normal, diploid SHE cells versus those of related, but transformed aneuploid cells. Highly synchronized cultures of these 2 cells were mutagenized by pulse treatment with BrdU during different periods of S phase, followed immediately by near-UV irradiation. The induced mutation frequencies so obtained provided information about the temporal order of replication of genes encoding HPRT and Na⁺/K⁺ ATPase in both SHE and BP6T cells. The temporal pattern of replication of Na⁺/K⁺ ATPase gene loci is similar in both cell types, but the temporal order of replication of the HPRT gene is significantly different between SHE and BP6T cells (mid-late S phase, versus early S phase, resp.). This observed difference emphasizes the caution required in the study of mutagenesis and DNA replication using transformed, aneuploid cells under the assumption that the underlying mechanisms are the same for normal, diploid cells.     

Separation of metabolic and non-metabolic steps of Rb+ uptake in spring wheat roots with different K+ status

Uptake of Rb⁺ from a complete nutrient solution with 2.0 mM Rb⁺ was studied in roots of spring wheat seedlings ( Triticum aestivum L. cv. Svenno) with different K⁺ levels. The relationship between Rb⁺ uptake and concentration of K⁺ in the roots indicated a negative feedback mechanism operating through allosteric control. The Rb⁺ uptake process in root cells was divided into two steps: (1) binding of the ion in the free space, and (ii) transmembrane transport into the cytoplasm. Metabolic and non-metabolic components of uptake were separated by addition of the metabolic inhibitor 2,4-dinitrophenol (DNP) to the nutrient solution. It is suggested that metabolic Rb⁺ uptake requires energy in two uptake steps (for binding to the carrier entity in the free space and for transmembrane transport) or in one step only (for transmembrane transport), dependent on the K⁺ status of the roots. The change from metabolic to non-metabolic binding in the free space is accomplished by changing the conformational state of the carrier (slow/fast transitions). There may be a hysteretic effect on metabolic Rb⁺ uptake through a slow transition between carrier states. This is superimposed on the negative cooperativity, strengthening further cooperativity at intermediate K⁺ levels in the roots. Non-metabolic Rb⁺ uptake probably consists of two components, a carrier-mediated (facilitated diffusion) and a parallel diffusive component.     

Regulation of asparaginase, glutamine synthetase, and glutamate dehydrogenase in response to medium nitrogen concentrations in a euryhaline chlamydomonas species

The ammonium assimilatory enzymes glutamine synthetase (EC 6.3.1.2) and glutamate dehydrogenase (EC 1.4.1.3) were investigated for a possible role in the regulation of asparaginase (EC 3.5.1.1) in a Chlamydomonas species isolated from a marine environment. Cells grown under nitrogen limitation (0.1 millimolar NH(4) (+), NO(3) (-), or l-asparagine) possessed 6 times the asparaginase activity and approximately one-half the protein of cells grown at high nitrogen levels (1.5 to 2.5 millimolar). Biosynthetic glutamine synthetase activity was 1.5 to 1.8 times greater in nitrogen-limited cells than cells grown at high levels of the three nitrogen sources.Conversely, glutamate dehydrogenase (both NADH- and NADPH-dependent activities) was greatest in cells grown at high levels of asparagine or ammonium, while nitrate-grown cells possessed little activity at all concentrations employed. For all three nitrogen sources, glutamate dehydrogenase activity was correlated to the residual ammonium concentration of the media after growth (r = 0.88 and 0.94 for NADH- and NADPH-dependent activities, respectively).These results suggest that glutamate dehydrogenase is regulated in response to ambient ammonium levels via a mechanism distinct from asparaginase or glutamine synthetase. Glutamine synthetase and asparaginase, apparently repressed by high levels of all three nitrogen sources, are perhaps regulated by a common mechanism responding to intracellular nitrogen depletion, as evidenced by low cellular protein content.