Lipoic acid content of Escherichia coli and other microorganisms

A mutant strain of Escherichia coli K12 requiring lipoic acid, W1485 lip 2 (ATCC 25645), was used to develop a turbidimetric assay for lipoic acid and a polarographic assay based on the oxidation of pyruvate by suspensions of lipoic acid-deficient organisms. The turbidimetric assay was more sensitive with a working range equivalent to 0.2–2.0 ng of dl-α-lipoic acid compared with 5–50 ng for the polarographic method. The mutant responded equally to racemic mixtures of α-lipoic acid, β-lipoic acid and dihydrolipoic acid but gave little response to lipoamide, and other derivatives without prior hydrolysis; 8-methyllipoic acid was a competitive inhibitor of the response to lipoic acid. A high specificity of the mutant for the natural stereoisomer was indicated by the fact that (+)-α-lipoic acid had twice the activity of the racemic mixture. Escherichia coli K12 contained less than 0.05 ng of free (+)-α-lipoic acid per mg dry weight but, depending on the growth substrate, the equivalent of between 13 and 47 ng of (+)-α-lipoic acid per mg dry weight after acid extraction. There was a strong correlation between the lipoic acid content and the sum of the specific activities for the pyruvate and α-ketoglutarate dehydrogenase complexes. Experiments with washed suspensions of Escherichia coli showed only small increases in lipoic acid content (18%) when incubated with pyruvate, cysteine and methionine. When supplied with exogenous lipoic acid the mutant, W1485 lip 2, accumulated very little more than was demanded by its metabolism. The lipoic acid contents of several organisms were measured and correlated with their metabolism.     

Prostaglandin-induced enhancement of the anamnestic response

The ability of various prostaglandins (PGs) to affect the anamnestic immune response of keyhole limpet hemocyanin (KLH)-primed rabbit popliteal lymph node cells was investigated. Of the four PGs studied (PGA₁, PGE₂ and PGF_2α), PGE₁ was found to have a stimulatory effect, whereas PGA₁, PGE₂ and PGF_2α were ineffective in stimulating or inhibiting the anamnestic response. Under the conditions studied, a 3.5-fold increase in antibody production was obtained in PGE₁-treated, KLH-stimulated cultures. Maximum enhancement was obtained when 0.2 μg of PGE₁ were added at the time of culture initiation and were allowed to remain in contact with the lymph node cells for 24 hours.     

Correction to: Integrative transcriptomics reveals genotypic impact on sugar beet storability

Plant Molecular Biology - In the above mentioned publication, part of Fig. 6B was distorted (extra diagonal lines appeared). The original article has been corrected and the proper version...     

Benzoylphenyl ureas inhibit chitin synthesis without interfering with amino sugar uptake in imaginal wing discs of Plodia interpunctella (Hübner)

We tested the hypothesis that the inhibition of chitin synthesis by benzoylphenyl ureas could be explained by their effect on the uptake of GlcNAc into chitin. Our test system consisted of organ cultures of wing imaginal discs from Plodia interpunctella. These wing discs synthesize chitin in response to 20-hydroxyecdysone or RH 5849, a non-steroidal ecdysteroid mimic. Two benzoylphenyl ureas, diflubenzuron and teflubenzuron, inhibited ecdysteroid-dependent chitin synthesis in the wing discs. However, although chitin synthesis was inhibited, there was no corresponding diminution of amino sugar uptake by the imaginal discs. In another experiment 20-hydroxyecdysone stimulated uptake of two sugars, 2-deoxy-D-glucose and 3-O-methyl-D-glucose, which are not synthesized into chitin. Transport of these non-metabolized sugars was unaffected by the inhibitors. In an additional test of the effects on precursor transport, the action of ecdysone (alpha-ecdysone) was examined. Ecdysone stimulated amino sugar uptake, but not chitin synthesis. Neither diflubenzuron nor teflubenzuron inhibited ecdysone-dependent precursor transport. Finally, we examined ecdysteroid-induced uptake of amino sugars by an imaginal disc derived cell line IAL-PID2. In this case, also, GlcNAc transport was not inhibited significantly by either diflubenzuron or teflubenzuron. From these observations we conclude that inhibition of uptake of amino sugars does not account for the ability of teflubenzuron and diflubenzuron to inhibit chitin synthesis in P. interpunctella wing discs.     

Second‐generation decline: Scenarios for the economic and ethnic futures of the post‐1965 American immigrants

‘Second‐generation decline’ questions the current American faith in the myth of nearly automatic immigrant success. In discussing economic scenarios, positive and negative, for the future of the children of the post‐1965 immigrants, the possibility is proposed that a significant number of the children of poor immigrants, especially dark‐skinned ones, might not obtain jobs in the mainstream economy. Neither will they be willing ‐ or even able ‐ to take low‐wage, long‐hour ‘immigrant’ jobs, as their parents did. As a result, they (and young males among them particularly) may join blacks and Hispanics among those already excluded, apparently permanently, from the mainstream economy. The article also deals with the relations between ethnicity and economic conditions in the USA and with the continued relevance of the assimilation and acculturation processes described by ‘straight‐line theory’. This issue, as well as most others discussed, may also be salient for European countries experiencing immigration, especially those countries with troubled economies.