The T-T pyrimidine (6-4) pyrimidinone UV photoproduct is much less mutagenic in yeast than in Escherichia coli.

We have examined the mutagenic properties of the T-T pyrimidine (6-4) pyrimidinone UV photoproduct in Saccharomyces cerevisiae, transforming the yeast cells either with single-stranded vectors that carried this adduct at a unique site or with gapped duplex vectors in which the adduct was located within a 28 nt single-stranded region. In an earlier study with SOS-induced Escherichia coli, we found that this photoproduct is highly mutagenic, specifically generating 3' T-->C substitutions in >85% of replicated molecules, and ascribed this specificity to the formation of a stable guanine-pyrimidinone mispair via hydrogen bonds at N-3 and O-2. In contrast, this adduct is very much less mutagenic in yeast, with 60-70% of molecules being replicated accurately and only 12-20% of them exhibiting 3' T-->C substitutions. The enhanced accuracy may reflect the ability of a yeast DNA polymerase, but not E.coli DNA polymerase III, to trap the adduct in a configuration favorable for the formation of an adenine-pyrimidinone base pair.     

Human DNA helicase IV is nucleolin, an RNA helicase modulated by phosphorylation

The cDNA encoding human DNA helicase IV (HDH IV), a 100-kDa protein which unwinds DNA in the 5′ to 3′ direction with respect to the bound strand, was cloned and sequenced. It was found to be identical to the human cDNA encoding nucleolin, a ubiquitous eukaryotic protein essential for pre-ribosome assembly. HDH IV/nucleolin can unwind RNA-RNA duplexes, as well as DNA-DNA and DNA-RNA duplexes. Phosphorylation of HDH IV/nucleolin by cdc2 kinase and casein kinase II enhanced its unwinding activity in an additive way. The Gly-rich C-terminal domain possesses a limited ATP-dependent duplex-unwinding activity which contributes to the helicase activity of HDH IV/nucleolin.     

On the multiplicity of platelet prostaglandin receptors: II. The use of N-0164 for distinguishing the loct of action for PGI2, PGD2, PGE2 and hydantoin analogs

The ω-chain variant analogs of prostacyclin (PGI₂) and PGD₂ in which the n-amyl side-chain has been replaced by a cyclohexyl group have been prepared and their cardiovascular activities have been compared to those of BW-245C(Fig. 1)(1) a potent anti-aggregatory vasodilator bearing a cyclohexyl-terminated side-chain on a hydantoin skeleton. The cyclohexyl group has little effect on PGI₂, but converts PGD₂ to a long lasting hypotensive agent and increases the platelet anti-aggregatory potency of PGD₂ by a factor of 8. The prostaglandin antagonist N-0164 selectively blocks the anti-aggregatory actions of PGD₂, cyclohexyl-PGD₂, and BW-245C; with essentially no effect on PGI₂, cyclohexyl-PGI₂ and PGE₂ at comparably effective doses. The latter observation is contrary to an earlier report by MacIntyre (2,3), but supports the view that the anti-aggregatory effect of high doses of PGE₂ ($\text{EC}{}_{50}\text{=50μ}\text{M}$) is mediated by the PGI₂ receptor (4). The hydantoin acts at the platelet PGD₂ receptor.     

Extracellular enzymes of some additional fungi associated with mushroom culture

Twenty-four fungus isolates from the compost utilized in commercially growing Agaricus brunnescens were tested for their ability to produce extracellular enzymes involved in the degradation of cellulose, lignin and xylan, the major components of the straw of the compost. All 24 isolates were able to degrade carboxymethyl cellulose. Most were classified as weak or moderate producers of exo--glucanase. Twenty of the 24 were also able to hydrolyze filter paper, a crystalline cellulose. Nineteen of the 24 were able to hydrolyze xylan, a hemicellulose. The production of extracellular polyphenol oxidases was detected utilizing two tests; the blueing of alcoholic gum guaiacol, which indicates tyrosinase production, and the browning of malt extract-gallic acid agar, which indicates laccase production. Twenty produced tyrosinase, but only eight produced laccase. Agaricus brunnescens was also included in all of the tests. It produced exo--glucanase, hemicellulase, tyrosinase and lactase.     

Social behavior of captive,group-living Orangutans

The behavior of orang-utans (Pongo pygmaeus)was observed in two captive groups (one adult group, one juvenile group). Activity profiles,animal interactions, and compartmental spatial use for both adult-group and juvenile-group individuals were recorded over a 9-month period. Behavioral repertoires for both groups included large amounts of social activity. Equivalent amounts of social activity were found for each group. The social behavior of juvenile animals involved more active behavior such as play. The social behavior of the adult animals was more subtle, involving social monitoring and allogrooming. These results indicate that orangutans, at least when group-living in captivity, exhibit the potential to display social behavior which is apparently of greater frequency and complexity than that which has been observed in the wild. These findings suggest that the solitary behavior of wild orangutans is not a necessary characteristic of orangutan behavior. Under different environmental conditions orangutans appear to readily adapt socially, and, like other nonhuman primates,they have the capacity to exhibit complex and subtle social behavior. This report is based on part of a senior thesis submitted by Sara D. Edwards     

Inhibition of protohaem ferro-lyase in experimental porphyria. Isolation and partial characterization of a modified porphyrin inhibitor.

Rat adrenal 105,000 g supernatant contains two lipid moieties, 'lipid-I' and 'lipid-II' which contain non-esterified cholesterol and stimulate cholesterol side-chain cleavage in soluble or mitochondrial enzyme systems. Lipid-I contains relatively large low-density heat-stable particles, whereas lipid-II particles are smaller, more dense and heat-labile. Lipid-I and lipid-II can be separated from clear cytosol by ultracentrifugation and gel filtration respectively. Corticotropin plus cycloheximide treatment increases the non-esterified cholesterol concentrations in the lipid fractions, and stimulatory effects of lipids on cholesterol side-chain cleavage appear to correlate with non-esterified cholesterol concentrations therein. On addition of saturating amounts of cholesterol-rich lipid, pregnenolone synthesis and cholesterol binding to cytochrome P-450 are stimulated more in mitochondria from corticotropin-stimulated adrenals than in mitochondria from control or corticotropin-plus cycloheximide-stimulated adrenals. These results support the contention that the corticotropin-induced increase in mitochondrial cholesterol side-chain cleavage involves an increase in cholesterol utilization as well as an increase in cholesterol availability.     

Inhibition of protohaem ferro-lyase by N-substituted porphyrins. Structural requirements for the inhibitory effect.

N-Methyl mesoporphyrin was a powerful inhibitor of protohaem ferro-lyase in vitro, whereas N-ethyl mesoporphyrin and N-methyl coproporphyrin were not and neither was the newly described green pigment produced by giving rats ethylene. This suggests that the size of the substituent at a pyrrole nitrogen and also the number of carboxylic acid side chains of the substituted porphyrin are important for the inhibitory effect. Evidence that N-methyl mesoporphyrin inhibited the enzyme, whereas the ethylene-derived pigment did not, was also obtained in vivo.     

Inactivation of Hydrogenase in Cell-free Extracts and Whole Cells of Chlamydomonas reinhardi by Oxygen

O₂ irreversibly inactivates hydrogenase from Chlamydomonas reinhardi. The mechanism for the inactivation involves the reaction of one molecule of hydrogenase with one molecule of O₂ (or two oxygen atoms) in the transition complex of the rate-limiting step. The second order rate constant for this reaction is 190 atmospheres⁻¹ minute⁻¹ (1.4 × 10⁵ molar⁻¹ minute⁻¹). At levels above 0.01 atmosphere O₂, the increased numbers of O₂ molecules may compete for the site of inactivation hindering the proper orientation for inactivation of any one O₂ molecule and resulting in lowered rates of inactivation.     

Adenosine triphosphate-activated adenylate deaminase from marine invertebrate animals. Properties of the enzyme from lugworm (Arenicola cristata) body-wall muscle.

Adenylate deaminase (AMP aminohydrolase, EC 3.5.4.6) from lugworm (Arenicola cristata) body-wall muscle was partially purified by extraction in KCl solutions and chromatography on phosphocellulose. Enzyme activity was eluted from the column at two salt concentrations. Both forms show co-operative binding of AMP (Hill coefficient, h, 2.85) with s0.5 values of 20 mM and 15.6 mM. ATP and ADP act as positive effectors lowering h to 1.07 and s0.5 to 2mM. The apparent Ka (activation) for ATP was 1.5mM. GTP is an inhibitor with an apparent Ki of 0.12 mM. In vivo the ATP-activated adenylate deaminase is in the active form and may be regulated by changes in GTP concentrations. Adenylate deaminase may act as a primary ammonia-forming enzyme in ammonotelic marine invertebrates with the purine nucleotide cycle.     

Inhibition of haem synthesis caused by cobalt in rat liver. Evidence for two different sites of action.

Cobalt inhibits liver haem synthesis in vivo by acting at least two different sites in the biosynthetic pathway: (1) synthesis of 5-aminolaevulinate and (2) conversion of 5-amino-laevulinate into haem. The first effect is largely, if not entirely, due to inhibition of the activity of 5-aminolaevulinate synthase, rather than to inhibition of the formation of the enzyme. The second effect results from diversion of 5-aminolaevulinate into an unidentified liver pool with solubility properties similar to those of cobalt protoporphyrin.