Effect of Concentration and Temperature on Flow Properties of Alyssum homolocarpum Seed Gum Solutions: Assessment of Time Dependency and Thixotropy

Effects of different shear rates (14, 25, and 50 s⁻¹), gum concentrations (3%, 3.5%, and 4%), and temperatures (5–65 °C) on flow properties of Alyssum homolocarpum seed gum solutions were investigated using a rotational viscometer. The experimental data were fitted with three time-dependent rheological models, namely second-order structural kinetic model, Weltman model, and first-order stress decay model with a non-zero stress value. The rate constant and extent of viscosity strongly depended on the shear rate, gum concentration, and temperature. It was found that A. homolocarpum seed gum samples exhibited shear thinning and thixotropic behavior for all concentrations and temperatures. The amount of structural breakdown decreased with shear rate, but it did not have a general trend with concentration and temperature. The extent of thixotropy increased with increasing gum concentration and decreased with increasing temperature and shear rate. In this work, the decay rate constant generally increased with increasing shear rate; however, it did not have any trend with concentration and temperature.     

A comparison of the folding characteristics of free and ribosome-tethered polypeptide chains using limited proteolysis and mass spectrometry

The kinetics and thermodynamics of protein folding are commonly studied in vitro by denaturing/renaturing intact protein sequences. How these folding mechanisms relate to de novo folding that occurs as the nascent polypeptide emerges from the ribosome is much less well understood. Here, we have employed limited proteolysis followed by mass spectrometry analyses to compare directly free and ribosome-tethered polypeptide chains of the Src-homology 3 (SH3) domain and its unfolded variant, SH3-m10. The disordered variant was found to undergo faster proteolysis than SH3. Furthermore, the trypsin cleavage patterns observed show minor, but significant, differences for the free and ribosome-bound nascent chains, with significantly fewer tryptic peptides detected in the presence of ribosome. The results highlight the utility of limited proteolysis coupled with mass spectrometry for the structural analysis of these complex systems, and pave the way for detailed future analyses by combining this technique with chemical labeling methods (for example, hydrogen-deuterium exchange, photochemical oxidation) to analyze protein folding in real time, including in the presence of additional ribosome-associated factors.     

Ring chromosome 14. I. A case report on homogeneous r(14)

A ring chromosome derived from a no. 14 was observed, without mosaicism, in a 2-month-old male with craniofacial dysmorphism, retarded psychomotor development, seizures and retinal anomalies. Serum immunoglobulins concentrations were normal.