Transformation of leukotriene A4 methyl ester to leukotriene C4 monomethyl ester by cytosolic rat glutathione transferases

Six major basic cytosolic glutathione transferases from rat liver catalyzed the conversion of leukotriene A4 methyl ester to the corresponding leukotriene C4 monomethyl ester. Glutathione transferase 4-4, the most active among these enzymes, had a Vmax of 615 nmol X min-1 X mg protein-1 at 30 degrees C in the presence of 5 mM glutathione. It was followed in efficiency by transferase 3-4 which had a Vmax of 160 nmol X min-1 X mg-1 under the same conditions. Transferases 1-1, 1-2, 2-2 and 3-3 had at least 30 times lower Vmax values than transferase 4-4.     

A mechanism for the formation of inside-out membrane vesicles. Preparation of inside-out vesicles from membrane-paired randomized chloroplast lamellae

Inside-out thylakoid membrane vesicles can be isolated by aqueous polymer two-phase partition of Yeda press-fragmented spinach chloroplasts (Andersson, B. and Åkerlund, H.-E. (1978) Biochim. Biophys. Acta 503, 462–472). The mechanism for their formation has been investigated by studying the yield of inside-out vesicles after various treatments of the chloroplasts prior to fragmentation. No inside-out vesicles were isolated during phase partitioning if the chloroplasts had been destacked in a low-salt medium prior to the fragmentation. Only in those cases where the chloroplast lamellae had been stacked by cations or membrane-paired by acidic treatment did we get any yield of inside-out vesicles. Thus, the intrinsic properties of chloroplast thylakoids seem to be such that they seal into right-side out vesicles after disruption unless they are in an appressed state. This favours the following mechanism for the formation of inside-out thylakoids. After press treatment, a ruptured membrane still remains appressed with an adjacent membrane. Resealing of such an appressed membrane pair would result in an inside-out vesicle.If the compartmentation of chloroplast lamellae into appressed grana and unappressed stroma lamellae is preserved by cations before fragmentation, the inside-out vesicles are highly enriched in photosystem II. This indicates a granal origin which is consistent with the proposed model outlined. Inside-out vesicles possessing photosystem I and II properties in approximately equal proportions could be obtained by acid-induced membrane-pairing of chloroplasts which had been destacked and randomized prior to fragmentation. Since this new preparation of inside-out thylakoid vesicles also exposes components derived from the stroma lamellae it complements the previous preparation.It is suggested that fragmentation of paired membranes followed by phase partitioning should be a general method of obtaining inside-out vesicles from membranes of various biological sources.     

L-3-Phosphoglyceric acid,formed by ribulose-1,5-bisphosphate carboxylase,is the primary substrate for photorespiration: Experimental test of a hypothesis

Preparations of RuBP carboxylase are shown to carry out an oxygen dependent decarboxylation of L-3-phosphoglyceric acid. The product of this reaction is probably phosphoglycollate. L-3-phosphoglyceric acid, formed by RuBP carboxylase is therefore proposed to be the primary substrate for photorespiration.     

Periodate oxidation and alkaline degradation of heparin-related glycans

Heparin, heparan sulphate, and various derivatives thereof have been oxidised with periodate at pH 3.0 and 4° and at pH 7.0 and 37°. Whereas oxidation under the latter conditions destroys all of the nonsulphated uronic acids, treatment with periodate at low pH and temperature causes selective oxidation of uronic acid residues. The reactivity of uronic acid residues depends on the nature of neighbouring 2-amino-2-deoxyglucose residues. d-Glucuronic acid residues are susceptible to oxidation when flanked by N-acetylated amino sugars, but resistant when adjacent residues are either unsubstituted or N-sulphated. L-Iduronic acid residues in their natural environment (2-deoxy-2-sulphoamino-d-glucose) are resistant to oxidation, whereas removal of N-sulphate groups renders a portion of these residues periodate-sensitive. Oxidised uronic acid residues in heparin-related glycans may be cleaved by alkali, producing a series of oligosaccharide fragments. Thus, periodate oxidation-alkaline elimination provides an additional method for the controlled degradation of heparin.     

Effect of Mg2+ and spermine on the kinetics of Ca2+ transport in rat-liver mitochondria

Plots relating the initial rate of mitochondrial Ca²⁺ transport to the Ca²⁺ concentration (kinetic plots) have a hyperbolic shape in a Ca²⁺ concentration range of 2.5–100 µM as measured in sucrose or KCl media. In the presence of Mg²⁺ or a polyamine spermine, which both are competitive inhibitors of Ca²⁺ binding to low affinity sites at the membrane surface, the shape of the plots becomes sigmoidal. At higher concentrations of these agents linear kinetic plots are obtained as measured in a sucrose medium. In a KCl medium the sigmoidality of the kinetic plots is enhanced by an increase in the Mg²⁺ or spermine concentration. It is suggested that Mg²⁺ and spermine affect the kinetics of Ca²⁺ transport by interfering with Ca²⁺ binding to low affinity sites of the membrane surface and that the binding of Ca²⁺ to these sites is the first step of the mitochondrial Ca²⁺ transport.     

LSD and related drugs as DA antagonists: Receptor-mediated effects on the synthesis and turnover of DA

We have earlier shown that d-lysergic acid diethylamide, LSD and its 2-bromo derivative, BOL like the dopamine (DA) antagonists haloperidol increased the rate of the $\text{in vivo}$ tyrosine hydroxylation in the striatum measured as the accumulation of DOPA after decarboxylase inhibition.Now we have found that several agents structurally similar to LSD increase the $\text{in vivo}$ tyrosine hydroxylation in the striatum. Psilocybin (50 mg/kg i.p.) and N,N-dimethyltryptamine (50 mg/kg i.p.) caused a short-lasting increase of DOPA accumulation, while mescaline (10 – 100 mg/kg i.p.) did not increase the DOPA accumulation. A marked increase of DOPA accumulation was observed after the 5-hydroxytryptamine (5-HT) antagonist cyproheptadine. The effects of LSD and structurally related drugs on the DOPA accumulation in the striatum appear to be mediated via DA antagonism at receptor level. However, these agents may control the DOPA accumulation via other receptors than DA receptors e.g. 5-HT receptors. A control of DOPA accumulation via receptors other than DA receptors appears to be predominant after treatment with N,N-dimethyltryptamine or psilocybin.     

Methionine adenosyltransferase activity in cultured cells and in human tissues

We have investigated methionine adenosyltransferase activity (MAT) in extracts of a variety of normal and malignant human tissues and cultured cell lines. MAT activity assayed from 17 different cultured cell lines varied to a great extent. Ramos (human, Burkitt's lymphoma) and EL4 (mouse, T cell lymphoma) cell showed MAT activity near 300 pmol/mg per min. Daudi (human, Burkitt's lymphoma) and almost all monolayer cells had MAT activity below 100 pmol/mg per min. Human peripheral blood lymphocytes had MAT activity of 36 pmol/mg permin. The MAT activity of the cell lines can be related to doubling time: cell lines with short doubling times have much higher MAT activity than other cell lines. A large variation in MAT activity in different human tissues was observed. In autopsy samples MAT activity was highest in the brain and in the colon. Malignant tissue samples gave much higher MAT activity than normal tissues. Lung cancer (carcinoma squamocellulare pulmonis) had MAT activity of 30.7 pmol/mg per min, while in normal lung it was 2.4 pmol/mg per min.     

The effects of parasitic water mite larvae (Arrenurus spp.) on zygopteran imagoes (Odonata)

Arrenurus larvae, ectoparasitic on zygopteran imagoes, attach to the host's cuticle and tear it to obtain the host's tissue fluids. Within the host's epidermis, each larval mite produces a feeding device, the stylostome, a narrow gelatinous resilient blind sac. Heavy mite infestation brings about several wounds in close proximity, accompanied by loss of more or less extensive areas of the epidermis. Despite wound repair by congregating hemocytes, local lack of epidermis seems to enfeeble the host, presumably owing to desiccation. Heavily mite-loaded zygopterans have lost the typical agility and are easily caught. A mite-induced mortality seems to exist in zygopteran populations; the infestation contributes to reduced longevity. The study of formation and decline of the arrenurid stylostome in zygopterans renders it possible to trace cellular defence reactions under natural conditions. Most stylostomes seem to thwart the ability of the host to recognize them as foreign bodies. The host's defence appears as a two-step reaction: (1) initial hemolymph clotting and deposition of melanin associated with aggregating hemocytes at the penetration site, (2) occasional subsequent melanization and cellular encapsulation of the stylostome.     

Sterols and steryl esters in some Brassica and Sinapis seeds

The qualitative and quantitative composition of sterols in the free form and esterified to fatty acids was studied in seed oils from Brassica napus, B. campestris, B..iuncea, B. nigra, Sinapis alba and S. aruefisis (Brassica kaber). Sitosterol, followed by campesterol, predominated in both the free and the esterified sterols. The free sterols were richer in brassicasterol (ca 10–20%) than the steryl esters (3–10%). Small amounts of δ⁵-avenasterol and δ⁷-stigmastenol were also found in the Brassica oils, often more in the esterified than in the free form. The quantity of sterols was studied only in Brassica campestris, which had ca 0.3 % in the free as well as in the esterified form. In Sinapis alba, ca 10% of the sterols in the free form and 20 % in the esterified sterols were δ⁵-avenasterol. This compared to only a few per cent in both the free and esterified sterols in the Brassica oils. Similarly, ca 2 % of cholesterol was found among the sterols of Sinapis alba but only traces in the Brassica oils. The similarity of sterol compositions among the cultivated brassicas and wild mustard (Sinapis arvensis), and the specific characteristics of the sterols in white mustard (Sinapis alba) adds further weight to the suggestion that wild mustard should be treated as Brassica kaber and strengthens the generic separation of Sinapis alba.     

Digestion and absorption of trioleoyl-thioglycerol in the rat

A triacylglycerol analogue, rac-1,2-di-O-oleoyl-3-S-oleoyl-3-thioglycerol, was fed to rats and chyle acylglycerols were analyzed. Triacylglycerol was the dominating chyle lipid but X-triacyl-1-thioglycerol constituted approx. 6% of total chyle lipids. Its identity was verified by ultraviolet and mass spectra and its stereochemical structure by ORD and CD. The proportions of triacyl-1-thio-sn-glycerol/triacyl-3-thio-sn-glycerol were $\text{63}\text{37}$ and $\text{78}\text{22}$ in two experiments. Possible reasons for this stereospecificity are discussed. The study shows that the stereochemical configuration of lipids isolated from biological material can be assessed by ORD and CD.