Early stages of LDL oxidation: apolipoprotein B structural changes monitored by infrared spectroscopy.

Changes in the conformation of apoliprotein B-100 in the early stages of copper-mediated low density lipoprotein oxidation have been monitored by infrared spectroscopy. During the lag phase no variation in structure is observed, indicating that copper binding to the protein does not significantly affect its structure. In the propagation phase, while hydroperoxides are formed but the protein is not modified, no changes in secondary structure are observed, but the thermal profile of the band corresponding to alpha-helix is displaced in frequency, indicating changes in tertiary structure associated with this conformation but not with beta-sheet components. When aldehyde formation starts, a decrease of approximately 3% in the area of bands corresponding to alpha-helix and beta-sheet is produced, concomitantly with an increase in beta-turns and unordered structure. The two bands corresponding to beta-turns vary as well under these conditions, indicating changes in these structures. Also at this stage the thermal profile shows variations in frequency for the bands corresponding to both alpha-helix and beta-sheet. The results are consistent with the hypothesis that as soon as the polyunsaturated fatty acids from the particle core are modified, this change is reflected at the surface, in the alpha-helical components contacting the monolayer.

Exogenously incorporated ketocarotenoids in large unilamellar vesicles. Protective activity against peroxidation.

The ability of astaxanthin and canthaxanthin as chain-breaking antioxidants was studied in Cu(2+)-initiated peroxidation of phosphatidylcholine large unilamellar vesicles (LUVs). Both carotenoids increased the lag period that precedes the maximum rate of lipid peroxidation, though astaxanthin showed stronger activity. For these experiments, different amounts of xanthophylls were exogenously added to previously made LUVs, non-incorporated pigment being afterwards removed. Differential scanning calorimetry assays with L-beta,gamma-dimyristoyl-alpha-phosphatidylcholine LUVs demonstrated that xanthophylls incorporated as described interact with the lipid matrix becoming interspersed among the phospholipid molecules.

[Proteolytic susceptibility of alpha-amylase of the pancreas of swine deprived of its structural calcium]. / Susceptibilidad proteolítica de la alpha-amilasa de páncreas de cerdo privada de su calcio estructural.

Hog pancreas alpha-amylase (alpha-1-4-glucan-glucan hydrolase, E.C. 3.2.1.1) lost its structural calcium by action of EDTA at 20 degrees C. Enzymatic activity experimented a decrease whereas a big increase in proteolytic susceptibility to bovine pancreas trypsin (E.C. 3.4.4.4) was shown. Native alpha-amylase had an activity of 2,730 mg maltose/min X mg enzyme and a Km of 0.222% amylose, the activity of calcium depleted amylase being of 1,640 mg maltose/min X mg enzyme and Km 0.571% amylose. Simple methods for evaluating proteolytic susceptibility of alpha-amylase micro-amounts against trypsin action, and for the measurement of alpha-amylase activity in polyacrylamide rod gels were also described.

Characterization of a carotenoprotein from the carapace of the crab Macropipus puber.

An orange carotenoprotein (lambda max = 480 nm) containing astaxanthin as prosthetic group was extracted and purified from the carapace of the crab Macropipus puber. The extraction was made possible by means of Triton X-100, yielding an orange carotenoprotein, with a molecular weight of about 56,000. Sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated only a single polypeptide of 14,000 daltons, suggesting that the orange caroteno-protein was a tetrameric form.