Glycosyl transferases in mouse and human milk fat globule membranes

Summary Membranes isolated from mouse and human milk fat globules were found to contain the enzymes responsible for the synthesis of dolichol monophosphate mannose and dolichol monophosphate glucose as well as those involved in the transference of the glycosyl residues from the two dolichol derivatives to dolichol diphosphate oligosaccharides. The levels of most of the enzymes were comparable to those found in mouse mammary gland microsomes. The presence of enzymes involved in protein glycosylation via dolichol derivatives in the milk fat globule membrane provides evidence in favor of an outward flow of membrane components from the rough endoplasmic reticulum, where these enzymes are active in vivo, towards the cell surface.     

Effect of lipids on activity and conformation of lysolecithin:lysolecithin acyltransferase from rabbit lung

Summary Lysolecithin:lysolecithin acyltranferase is an enzyme which in several previous studies has shown a dual behavior catalyzing two types of reaction, transacylation or hydrolysis, with the same substrate. Both activities have shown to be dependent on several environmental conditions and among them, the presence of lipids.The addition of several classes of lipids activated in all the cases the enzyme, decreasing the hydrolysis/transacylation molar ratio. This effect was higher for PC/PE/Chol mixture than for other lipids assayed. Circular dichroism spectra of the enzyme did not show any change with the addition of lipids, concluding that the effect of lipids was not due to any structural change in the protein. The hypothesis has been made of an influence of lipids on the physical state of the substrate as well as, possibly, on the enzyme-substrate interaction.The significance of these effects on the physiological role of lysolecithin:lysolecithin acyltransferase from soluble fraction of rabbit lung is discussed.Abbreviations Chol cholesterol - CMC critical micellar concentration - DPPC dipalmitoylphosphatidylcholine - FA fatty acid - H/T hydrolysis/transacylation molar ratio - LPC lysophosphatidylcholine - PC phosphatidylcholine - PE phosphatidylethanolamine - TG triglyceride - UV ultraviolet     

S-adenosylmethionine and morphogenesis inMucor racemosus

The intracellular concentration of S-adenosylmethionine (SAM) and the specific activity of S-adenosylmethionine synthetase (ATP:l-methionine S-adenosyltransferase, EC 2.5.1.6) were examined in wild-typeMucor racemosus, as well as a morphological mutant termedcoy, under conditions designed to prevent the morphogenesis of yeasts to hyphae. When the mutant was grown in a defined medium supplemented with methionine and induced to shift by exposure to air, there was an increase in intracellular SAM analogous to that previously reported with the wild type. However, when thecoy mutant was grown in the absence of methionine, the intracellular concentration decreased dramatically and the mutant failed to undergo the yeast to hypha transition. An inhibitor of SAM synthetase activity, cycloserine, was used to lower the intracellular concentration of SAM in the wild-type organisms. Under these conditions, wild-typeM. racemosus failed to undergo the transition from yeasts to hyphae when exposed to air.     

Role of adrenergic innervation in experimental renal hypertension

Renal hypertension was induced by ligation of the aorta between renal arteries in rats sympathectomized with 6-hydroxydopamine. In the early phase, equally severe hypertension developed in the denervated group as compared to innervated controls. Later, blood pressure was lower in the denervated rats. Initially, increases in plasma renin were seen in both groups; the levels, however, were markedly lower in the denervated rats. Later, the renin levels were similar and not different from baseline. It is concluded that adrenergic neural activity is not essential in the development of renal hypertension; the maintenance of the chronic state, however, depends in part on adrenergic innervation.     

Differences in blastema-associated proteins according to position along body axis in regenerating planarians

To test the hypothesis that neoblasts in different positions in regenerating pieces of planarians may be differentially responsive to diffusible stimuli through differentially expressed membrane receptors, we compared membrane surface proteins in blastemas induced at various positions along an anterior-posterior axis in Dugesia gonocephala (Dugès). The proteins were biotinylated and identified by molecular weight in SDS-PAGE (sodium-dodecylsulfate polyacrilamide gel electrophoresis). This SDS-PAGE pattern was then compared with that of N-glycosylated proteins incorporating ³H-mannose. One 20 kDa glycoprotein present in all blastemas at 3 d was absent from more anterior blastemas at 6 d irrespective of whether those blastemas were at the cephalic or the caudal end of the regenerating piece. The expression of this protein appears to be determined by the position of the blastema along the body axis rather than by its prospective fate.     

Transformation of Acidiphilium by electroporation and conjugation.

Two techniques, electroporation and conjugation, have been used to introduce the RK2-based broad-host-range plasmids pRK415 and pLAFR3 into strains of the bacterial genus Acidiphilium. Using electroporation, cells were also transformed with a series of chimeric plasmids constructed by cloning cryptic Acidiphilium plasmids into the Escherichia coli vector pBR328. Various parameters affecting electroporation were investigated. Transformation efficiency varied widely with different recipient strains. Growth at an elevated temperature (37 degrees C) prior to electroporation increased transformation efficiency 10-fold compared with growth at 32 degrees C. For three strains tested, optimum transformation efficiency was obtained with field strengths of 10-15 kV/cm. Transformation efficiency increased linearly with increasing DNA concentration up to 10 micrograms/mL. Transformation efficiencies in these experiments ranged up to 10(4) transformants/micrograms DNA. Mobilization of pRK415 and pLAFR3 from E. coli strain S17.1 into several Acidiphilium strains was achieved following incubation for 3 h on nutrient agar medium (pH 7.0). Conjugation frequencies in the range of 10(-5)-10(-9) per recipient cell were obtained. Conjugation frequency was also dependent on recipient strain.     

Kiwifruit micropropagation through callus shoot-bud induction

Summary A profitable system for the establishment of morphogenic callus cultures and indirect shoot induction and development was accomplished from nodal shoot segments obtained from adult and micropropagated plants of kiwifruit (Actinidia deliciosa [Chev.] Liang and Ferguson, var.deliciosa) cv. “Hayward”. The effects of medium composition, cytokinin levels, dilution of salts, and type of callus derived from the cultured primary explants were studied. Medium composition as well as type of callus greatly affected organogenic responses.     

Peripheral nervous control of cold-induced reduction in the respiratory quotient of the rat

Cold-exposed rats show a reduction in the respiratory quotient which is indicative of a relative shift from carbohydrates to lipids as substrates for oxidative metabolism. In the present study, the effects of food deprivation and cold exposure on the respiratory quotient were observed. In addition, the involvement of the three main branches of the peripheral nervous system (sympathetic, parasympathetic, and somatic) was investigated by means of synaptic blockade with propranolol, atropine, and quinine, respectively. Both propranolol and quinine blocked the cold-induced decrease in respiratory quotient and increase in heat production, whereas atropine had only minor and very brief effects. It is concluded that both the sympathetic and somatic branches are involved in the metabolic changes associated with cold-induced thermogenesis and that the increase in metabolic heat production involves a shift from carbohydrate to lipid utilization irrespective of which of the two branches is activated.