Michael David Winther

Activity of human Δ5 and Δ6 desaturases on multiple n-3 and n-6 polyunsaturated fatty acids

Yeast co‐expressing human elongase and desaturase genes were used to investigate whether the same desaturase gene encodes an enzyme able to desaturate n‐3 and n‐6 fatty acids with the same or different carbon chain length. The results clearly demonstrated that a single human Δ5 desaturase is active on 20:3n‐6 and 20:4n‐3. Endogenous Δ6 desaturase substrates were generated by providing to the yeast radiolabelled 20:4n‐6 or 20:5n‐3 which, through two sequential elongations, produced 24:4n‐6 and 24:5n‐3, respectively. Overall, our data suggest that a single human Δ6 desaturase is active on 18:2n‐6, 18:3n‐3, 24:4n‐6 and 24:5n‐3.

Spermine, Spermidine and Putrescine in Fungal Development

Publisher Summary A number of different naturally-occurring oligoamines exist but only three are known to be widely distributed—namely, putrescine (1,4-diaminobutane), spermidine (4 azaoctane- 1,8-diamine), and spermine (4,9 diazadodecane-l,12-diamine). Because there is a correlation among oligoamine synthesis, cell growth, and differentiation and as the latter process cannot be easily studied in bacteria, fungi have a number of advantages in studying differentiation. Fungi exhibit a wide variety of developmental patterns many of which can be varied under laboratory conditions. Also, extensive genetic analysis can often be carried out on fungi. They are suitable phyllum for studying the role of oligoamines in development, and this helps to solve the more general question of oligoamine function. The chapter discusses the distribution and biosynthesis of oligoamines with particular emphasis on the contrast between prokaryotes and eukaryotes. Oligoamine distribution and synthesis in fungi, and related amino-acid biosynthesis is presented. Fungal development, with emphasis on correlations among nucleic acid, protein, and oligoamine synthesis, is also discussed.

The effects of 1,4-diaminobutanone on polyamine synthesis in Aspergillus nidulans

The naturally occurring polyamines, putrescine, spermidine and spermine are synthesized in most eucaryotes from ornithine and methionine [ 1,2] by the pathway outlined in fig. 1. The functions of these amines which often occur in millimolar concentrations [ 1,2] are unknown. They are synthesized most rapidly in proliferating cells [2]. In order to try to establish their functions much work has recently focussed on the development of specific inhibitors of polyamine synthesis [3-l 11. Putrescine occupies a central position in the synthesis of spermidine and spermine: (i) It has been found to inhibit the production of ornithine decarboxylase [12-l 71 (ii) It is a weak competitive inhibitor of ornithine decarboxylase [ 17-20 J (iii) It is an activator of S-adenosyl methionine decarboxylase [ 17,20-231 (iv) It is a substrate for spermidine synthase [ 1,2] (v) It is a competitive inhibitor of spermine synthase [241. During a search for a gratuitous repressor of ornithine decarboxylase such as has now been found for this enzyme in regenerating liver [25] we tested a number of compounds having structures similar to putrescine and found that one of these, 1:4 diaminobutanone, stimulated the increased production of ornithine decarboxylase in germinating conidia of Aspergillus nidulans. On further examination this compound was found to be a powerful competitive inhibitor of ornithine decarboxylase, it could replace putrescine as an activator of S-adenosyl methionine decarboxylase, and it also caused a reduction in the intracellular concentrations of spermidine and spermine.

Lithium γ-linolenate-induced cytotoxicity against cells chronically infected with HIV-1

Lithium γ‐linolenate (Li‐GLA), was evaluated for its activity in selectively killing H9 cells chronically infected with HIV‐1RF. After 4 days incubation with Li‐GLA approximately 90% of the H9RF cells were non‐viable compared to 20% of uninfected H9 cells. The efficacy of the Li‐GLA, in preferentially killing HIV infected cells also correlates with lipid peroxidation, as measured by the intracellular thiobarbituric acid‐reactive material content. The addition of an antioxidant (vitamin E) to the culture medium reduced the toxicity of Li‐GLA. These data indicate that this selective killing effect of cells chronically infected with HIV may be due to the enhanced extent of lipid peroxidation of the added Li‐GLA.

Activity and mRNA abundance of Δ-5 and Δ-6 fatty acid desaturases in two human cell lines

We analyzed fatty acid biosynthesis in Chang and ZR‐75‐1 cells. Both cell lines could desaturate and further elongate substrates for Δ‐5 desaturase. ZR‐75‐1 but not Chang cells showed Δ‐6 desaturation of 18:2n‐6, 18:3n‐3, 24:4n‐6 and 24:5n‐3. In both cell lines, the mRNA abundance can be related to Δ‐5 or Δ‐6 fatty acid desaturase activities. These results suggest that desaturase genes could have, at least in part, independent control mechanisms and that Δ‐6 desaturase impairment is not specific to any particular step of the fatty acid metabolic pathways, which may diminish the rationale for the existence of at least two distinct enzymes.

Polyamine stimulation of in vivo rates of macromolecular synthesis in a putrescine auxotroph of Aspergillus nidulans

(NH*-(CH&-NH& spermidine (NH&CH&- NH-(CH&-NH2) and spermine (NH,-(CH&- NH-(CHz)4-NH-(CH&-NH2) are ubiquitous cations whose precise physiological roles remain unclear. It has been proposed that polyamines are involved in the synthesis of nucleic acids and proteins and/or maintaining membrane stability [ 11. Investiga- tions of E. coli polyamine auxotrophs have demon- strated a role for polyamines in protein synthesis that is independent of transcription [2,3]