Chromatographic purification and characterization of B-phycoerythrin from Porphyridium cruentum. Semipreparative high-performance liquid chromatographic separation and characterization of its subunits

A fast preparative two-step chromatographic method for purification of B-phycoerythrin from Porphyridium cruentum is described. This biliprotein was homogeneous as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis yielding three closely migrating bands corresponding to its three subunits. Baseline separation of its alpha-, beta- and gamma-subunits was achieved by a reversed-phase HPLC gradient semipreparative method with a C4 large-pore column and a solvent system consisting of 0.05% trifluoroacetic acid (TFA) in water and 0.05% TFA in acetonitrile. B-Phycoerythrin in different aggregation states and its subunits have been spectroscopically characterized. Hexameric B-phycoerythrin has similar secondary and tertiary structure than dissociated B-phycoerythrin determined by circular dichroism.

Fluorescence-labelled DNA probes to detect complementary sequences in homogeneous media

Sensitive, safe and easy-to-use probes for the detection of nucleic acids are urgently called for. To this end we are in the process of developing a fluorescence-based technique to work in homogeneous assay media. We have examined pyrene and fluorescein as fluorescent labels for natural DNA probes. A fraction of the cytosine residues of a single-stranded cDNA was randomly labelled with either pyrene or fluorescein using the bisulfite-catalyzed diamine reaction. Both fluorophores showed fluorescence quenching when the labelled probe was hybridized with its complementary strand and we describe the changes in steady-state fluorescence intensity that occurred upon hybridization. Our results demonstrate that pyrene quenching is more efficient than fluorescein quenching and thus pyrene-labelled probes are more sensitive for detecting and quantifying DNA from natural sources.

Changes in chemical composition and physico-chemical properties of chick low- and high-density lipoproteins induced by supplementation of coconut oil to the diet

Supplementation of coconut oil to the diet for 1-2 weeks produced a significant hypercholesterolemia in 14-day-old chicks. Changes in plasma fatty acid composition correlated positively with those of diets. In this study, we have shown a different response of low- and high-density lipoprotein (LDL and HDL) fractions to dietary saturated fat (coconut oil) rich in lauric and myristic acids. Although all the components of these particles seemed to increase, the percentages of increases found in total (TC), free (FC) and esterified cholesterol (EC) were higher in LDL than in HDL. TC/phospholipid (PL) ratio, considered as an inverse index of membrane fluidity, also increased with the dietary regimen in LDL, while no significant differences were found in HDL. These results suggest that supplementation of coconut oil to the diet decreased the fluidity of LDL. The EC/triglycerides (TG) ratio was also significantly increased in LDL, corroborating the main atherogenic function of this lipoprotein fraction in response to lauric and myristic acids. We have also estimated the lipidic order parameter, S, from the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH)-labelled low- and high-density lipoproteins. In LDL, temperature dependence of S shows two different behaviour zones at about 20 degrees C. In HDL, the plot of S values versus T is linear. DPH anisotropy and S increased in both LDL and HDL from treated chicks. This increase becomes more evident as temperature rises and also with dietary treatment.