The formation, isolation and importance of isopeptides in heated proteins

Texturization of a Blend of Pea and Destarched Oat Protein Using High-Moisture Extrusion

Grain protein fractions have great potential as ingredients that contain high amounts of valuable nutritional components. The aim of this study was to study the rheological behavior of destarched oat and pea proteins and their blends in extrusion-like conditions with a closed cavity rheometer. Additionally, the possibility of producing fibrous structures with high-moisture extrusion from a blend of destarched oat and pea protein was investigated. In the temperature sweep measurement (60-160 °C) of the destarched oat protein concentrate and pea protein isolate blend, three denaturation and polymerization sections were observed. In addition, polymerization as a function of time was recorded in the time sweep measurements. The melting temperature of grain proteins was an important factor when producing texturized structures with a high-moisture extrusion. The formation of fibrillar structures was investigated with high-moisture extrusion from the destarched oat and pea protein blend at temperatures ranging from 140 to 170 °C. The protein-protein interactions were significantly influenced in the extruded samples. This was due to a decrease in the amount of extractable protein in selective buffers. In particular, there was a decrease in non-covalent and covalent bonds due to the formation of insoluble protein complexes.

Increase of gamma-glutamyl-beta-alanyl-histidine isopeptide in the macromolecular fraction of model chicken extract during heating and distribution in commercial chicken extracts

Changes in the amino acid composition and contents of gamma-glutamyl-beta-alanyl-histidine isopeptide in the macromolecular fraction were measured during heating of chicken extract. Increases of histidine, 1-methylhistidine, and beta-alanine were observed, suggesting that carnosine and anserine were incorporated into the macromolecular fraction. The increase of gamma-glutamyl-beta-alanylhistidine isopeptide in the macromolecular fraction of chicken extract was also observed during the heating process. Furthermore, measurement of gamma-glutamyl-beta-alanylhistidine isopeptide in commercial chicken extract showed that all kinds of chicken extract contained the above isopeptide (from 0.09 to 0.31 micromol/g DM in the macromolecular fraction). These results suggest that the formation of gamma-glutamyl-beta-alanyl-histidine and related isopeptides occur during heating of chicken extract.

Isolation and chemical characterization of Alzheimer's disease paired helical filament cytoskeletons: differentiation from amyloid plaque core protein

The paired helical filaments (PHFs) of Alzheimer's disease were purified by a strategy in which the neurons and amyloid plaque cores of protein (APCP) were initially isolated. This was achieved by several steps of isocratic sucrose centrifugations of increasing molarity and a discontinuous isotonic Percoll density gradient. After collagenase elimination of contaminating blood vessels, lysis of neurons was produced by SDS treatment. The released PHF cytoskeletons were separated from contaminating APCP and lipofuscin by sucrose density gradient. A final step consisted in the chemical purification of highly enriched PHFs and APCP components via a formic acid to guanidine hydrochloride transition. PHFs and APCPs were fractionated by size exclusion HPLC and further characterized and quantitated by automatic amino acid analysis. We also present some of the morphological and immunochemical characteristics of PHF polypeptides and APCP. Our studies indicate that apart from differences in localization and morphology, PHF and APCP significantly differ in (a) chemical structure (peptide and amino acid composition); (b) epitope specificity (antiubiquitin, antitau, antineurofilament); (c) physicochemical properties (structural conformation in guanidine hydrochloride); and (d) thioflavine T fluorescence emission. These parameters strongly suggest important differences in the composition and, probably, in the etiopathology of PHF and APCP of Alzheimer's disease.