Inhibition of dihydropteridine reductase by dopamine

Dihydropteridine reductase has been purified 900-fold from rat liver. Dopamine inhibited the enzyme up to 50% at a concentration of 0.11mm. In the presence of dopamine the enzyme gave non-hyperbolic v-against-[S] plots. This enzyme may have a role in control of dopamine biosynthesis.     

Phenotypic instability in a tif-1 mutant of Escherichia coli

Summary A recent study showed that in E. coli T44 () carrying the tif-1 mutation, elevated temperature and adenine can interfere with the translation process. The present study shows that the expression of tif phenotypes (thermoinduction and filamentation) is suppressed by factors which affect ribosomal function. Ethanol suppresses thermoinduction and, in some spc ^r mutants, both thermoinduction and filamentation are suppressed. An unknown factor(s) in yeast extract suppresses both thermoinduction and filamentation. In thermoresistant revertant (ts⁺), the expression of the ts⁺ phenotype is suppressed by yeast extract, ethanol, guanosine+cytidine and by the addition of a spc ^r mutation. This indicates that this phenotype could be due to suppressor mutations, and the interaction between factors affecting ribosomal function and the ts⁺ phenotype suggests that the suppression of tif in the ts⁺ strains could operate on the ribosomal level. In vitro studies show that in extracts from either spc ^r or ts⁺ strains, or in the presence of ethanol, translational restriction is relieved, suggesting that the suppression of tif phenotypes could involve the translation process.     

Monolignol and dilignol glycosides from Pinus contorta leaves

Four monolignol glucosides have been isolated and identified from the needles of Pinus contorta. Chavicol 4-O-α-L-arabinofuranosyl-(1 →     

Inhibition of cholesterol esterases by Δ1-tetrahydrocannabinol

Δ¹-Tetrahydrocannabinol was found to inhibit the action of esterases derived from rat adrenal and luteinized ovary on exogenous cholesteryl palmitate. The drug was effective at a dose of 3.2μM causing greater than 30% inhibition; at 16μM almost complete inhibition occured. These findings are similar to those we have recently reported with mouse Leydig cells (1) showing that this is an effect common to steroidogenic tissues and raising the possibility that a variety of endocrine effects of this drug may be due to direct action on these tissues.     

Acylated flavonol glucosides of Pinus contorta needles

From fresh Pinus contorta Doug (Coastal) needles four flavonol acylated glucosides and 6-methyl-kaempferol 3-β-D-glucoside were isolated. The three monoacylated glucosides were kaempferol-3-β-D(6-O-p- coumaryl)glucoside, isorhamnetin-3-β-D-(6-O-acetyl)glucoside, quercetin-3-β-D-(p-coumaryl)glucoside and the diacyl compound was kaempferol-3-β-D-(di-p-coumaryl)glucoside.     

The role of transferrin and citrate in cellular uptake of aluminium

Summary The ability of human erythroleukaemia K562 cells to take up aluminium from Al-transferrin and Al-citrate has been examined. Uptake from Al-transferrin was dose-dependent over the range 68–544 ng/ml of aluminium, and increased over a 12-day period. In contrast, uptake from Al-citrate was low even at an aluminium concentration of 6800 ng/ml and did not increase over time. Neither form of aluminium greatly affected cell growth. It is concluded that Al-transferrin, rather than Al-citrate, is the physiologically relevant form of this metal with respect to cellular uptake, but that any metabolic abnormalities induced by aluminium do not affect proliferation of this cell line.     

Implications of life-history strategies for a new wrasse fishery

The variety of life-history patterns exhibited by the five species of wrasse common in Northern Europe are reviewed. The two larger wrasse species, the ballan, Labrus bergylta Ascanius, and cuckoo, Labrus mixtus (L.), are exploited through sport angling. The three smaller species, the corkwing, Symphodus (Crenilabrus) melops (L.), rock cook, Centrolabrus exoletus (L.) and goldsinny, Ctenolabrus rupestris (L.), are being exploited by a new fishery for use as parasite cleaners of farmed salmon.
The nature of salmon farming limits the wrasse fishery to a minimum size, restricted areas and the warmer months of the year. The fishery may be expected to alter population structure through selective removal of larger fish. Removal of dominant territorial males may affect social structures and removal of nest-guarding males would reduce egg survival. Quantitative models incorporating stock size and fishery requirements are now required.     

Evolutionary significance of the renal excretion of transferrin half-molecule fragments

It is generally thought that the duplicated structure of serum transferrin in vertebrates arose by gene duplication and fusion from a small ancestral protein. We have found that the isolated domains of transferrin are rapidly lost from the bloodstream via the kidneys. Therefore we suggest that the ancestral transferrin was not a serum protein or, alternatively, that it was not as small as the half-molecule.