Influence of Transglutaminase Crosslinking on Casein Protein Fractionation during Low Temperature Microfiltration

Low temperature microfiltration (MF) is applied in dairy processing to achieve higher protein and microbiological quality ingredients and to support ingredient innovation; however, low temperature reduces hydrophobic interactions between casein proteins and increases the solubility of colloidal calcium phosphate, promoting reversible dissociation of micellar β-casein into the serum phase, and thus into permeate, during MF. Crosslinking of casein proteins using transglutaminase was studied as an approach to reduce the permeation of casein monomers, which typically results in reduced yield of protein in the retentate fraction. Two treatments (a) 5 °C/24 h (TA) and (b) 40 °C/90 min (TB), were applied to the feed before filtration at 5 °C, with a 0.1 µm membrane. Flux was high for TA treatment possibly due to the stabilising effect of transglutaminase on casein micelles. It is likely that formation of isopeptide bonds within and on the surface of micelles results in the micelles being less readily available for protein-protein and protein–membrane interactions, resulting in less resistance to membrane pores and flow passage, thereby conferring higher permeate flux. The results also showed that permeation of casein monomers into the permeate was significantly reduced after both enzymatic treatments as compared to control feed due to the reduced molecular mobility of soluble casein, mainly β-casein, caused by transglutaminase crosslinking.

Coordinated conformational changes in the V1 complex during V-ATPase reversible dissociation

Vacuolar-type ATPases (V-ATPases) are rotary enzymes that acidify intracellular compartments in eukaryotic cells. These multi-subunit complexes consist of a cytoplasmic V1 region that hydrolyzes ATP and a membrane-embedded VO region that transports protons. V-ATPase activity is regulated by reversible dissociation of the two regions, with the isolated V1 and VO complexes becoming autoinhibited upon disassembly and subunit C subsequently detaching from V1. In yeast, assembly of the V1 and VO regions is mediated by the RAVE complex through an unknown mechanism. We used cryoEM of yeast V-ATPase to determine structures of the intact enzyme, the dissociated but complete V1 complex, and the V1 complex lacking subunit C. Upon separation, V1 undergoes a dramatic conformational rearrangement, with its rotational state becoming incompatible for reassembly with VO. Loss of subunit C allows V1 to match the rotational state of VO, suggesting how RAVE could reassemble V1 and VO by recruiting subunit C.

Power Grid Integration and Use-Case Study of Acid-Base Flow Battery Technology

There are many different types of energy storage systems (ESS) available and the functionality that they can provide is extensive. However, each of these solutions come with their own set of drawbacks. The acid-base flow battery (ABFB) technology aims to provide a route to a cheap, clean and safe ESS by means of providing a new kind of energy storage technology based on reversible dissociation of water via bipolar electrodialysis. First, the main characteristics of the ABFB technology are described briefly to highlight its main advantages and drawbacks and define the most-competitive use-case scenarios in which the technology could be applied, as well as analyze the particular characteristics which must be considered in the process of designing the power converter to be used for the interface with the electrical network. As a result, based on the use-cases defined, the ESS main specifications are going to be identified, pointing out the best power converter configuration alternatives. Finally, an application example is presented, showing an installation in the electrical network of Pantelleria (Italy) where a real pilot-scale prototype has been installed.

Reversible dissociation of singly-bonded (C60−)2 dimers in (MV˙+)2(C60−)2·solvent salt containing paramagnetic methyl viologen MV˙+ radical cations

Interaction of MV0 with C60 produces salt (MV˙+)2(C60−)2⋅solvent (1) containing singly-bonded (C60−)2 dimers dissociated at 235–375 K. There is exchange interaction between MV˙+ and C60˙− in the monomeric phase which is switched off in the dimeric phase.

Reversible regulation of metallo-base-pair interactions for DNA dehybridization by ultrasound

Ultrasound leads to the reversible dissociation of DNA metallo-base-pairs when these motifs are functionalized with oligodeoxynucleotide sequences of sufficient length.

A Steady-State Algebraic Model for the Time Course of Covalent Enzyme Inhibition

This report describes an algebraic equation for the time course of irreversible enzyme inhibition following a two-step mechanism. In the first step, the enzyme and the inhibitor associate reversibly to form a non-covalent complex. In the second step, the noncovalent complex is irreversibly converted to the final covalent conjugate. Importantly, the algebraic derivation was performed under the<i> steady-state approximation</i>. Under the previously invoked <i>rapid-equilibrium approximation</i> [Kitz & Wilson (1962) <i>J. Biol. Chem.</i> <b>237</b>, 3245] it is by definition assumed that the rate constant for the reversible dissociation of the initial noncovalent complex is very much faster than the rate constant for the irreversible inactivation step. In contrast, the steady-state algebraic equation reported here removes any restrictions on the relative magnitude of microscopic rate constants. The resulting formula was used in heuristic simulations designed to test the performance of the standard rapid-equilibrium kinetic model. The results show that if the inactivation rate constant is significantly higher than the dissociation rate constant, the conventional “kobs” method for evaluating the potency of covalent inhibitors in drug discovery is incapable of correctly distinguishing between the two-step inhibition mechanism and a simpler one-step variant, even for inhibitors that have very high binding affinity in the reversible noncovalent step.