Heat transfer proteins

Biochemical processes such as protein unfolding/refold-ing and supramolecular assembly/disassembly take place on a time scale of seconds to minutes after readjusting the temperature of a system. Most commercially available glass-jacketed cuvettes are not suitable for temperature jumps on this time scale, as a result of the slow kinetics of heat transfer across substances with characteristically high dielectric constants, and their use can convolute the time scale of the temperature change onto the time scale... 

Kriminski, S., Kazmierczak, M. and Thorne, R. E. (2003). Heat transfer from protein crystals impUcations for flash-cooling and X-ray beam heating. Acta Crystallogr. D 59,697-708. 

Cholesteryl ester transfer protein (CETP) promotes exchange and transfer of neutral lipids such as cholesteryl ester (CE) and TG between plasma lipoproteins [63-65], The function of CETP is illustrated in Fig. 3. CETP is a very hydrophobic and heat-stable glycoprotein with an apparent molecular weight of 74 kDa as determined by SDS-PAGE analysis [66,67], The cDNA from human liver was cloned and sequenced [68], It encodes for a 476-amino acid protein (53 kDa), suggesting that the apparent higher molecular weight is due to the addition of carbohydrate residues by posttranslational modification. 

Another plasma LTP (LTP-2), which facilitates transfer of phosphatidylcholine but not cholesteryl ester or triglyceride (A17, T2), is heat labile, losing 90% of its activity after incubation at 58°C for I hour (A17). This latter transfer protein has not been characterized in detail. 

Fig. 1. Intracellular events involved in steroid hormone action. A. Model in which the receptor is cytosolic and transfers tothe nucleus after binding with steroid (S). The cytosolic 8S receptor consists of a ligand binding unit ( ) and other units, one of which is a 90 kDa heat shock protein ( ). Activation is shown here as involving dimerisation of the ligand binding unit. This simplification of the true events applies to oestradiol receptor but not necessarily for other receptor classes. There is no agreement as to where activation occurs. B. Model in which unliganded receptor (0) is in the nucleus. A conformational change occurs on binding steroid (S) which may result in increased affinity for specific DNA sequences.

Zhou, V. et al. 2004. A time-resolved fluorescence resonance energy transfer-based HTS assay and a surface plasmon resonance-based binding assay for heat shock protein 90 inhibitors. Anal. Biochem. 331, 349-357. 

Often, foods must be treated as engineering materials. Heat has to be transported so that the components become cooked or harmful microorganisms and toxins become inactivated. Even in the kitchen, mixing involves the mass transfer of liquids and solids to form metastable structures, which are fixed by subsequent treatment by heat or cooling. Heat transfer properties are crucial in the formation of ice crystals in ice cream and fat crystals in chocolate products. Food materials have been used as a source of industrial components soybean proteins to manufacture auto parts in the 1940s, casein to make buttons and knitting pins, and starches in adhesives and thickeners. 

Analogously, Douglas et al. have used a small 24 subunit heat shock protein isolated from the hyperthermophilhc archaeon, Methanococcus jannaschii, as a biomimetic template for the oxidative mineralization of iron. Both the wild type and a mutant (glycine at position 41 replaced for cysteine) exhibited ferrihydrite mineralization as determined by an increase in the ligand to metal charge transfer absorbance at 400 nm and the presence of discrete iron oxide particles of... 

The Low power microwaves employed here do not perturb the plasmonic surfaces, do not produce arcing which is conunonly observed for metallic objects in microwave cavities,[56] or even denature or change protein conformation. Low power microwaves provide for effective rapid heating of the assays, producing identical final fluorescence intensities, fluorophore lifetimes, as well as extents of energy transfer (protein conformation) as compared to room temperature incubation. 

For instance, if ampules of aqueous products were to be sterilized in a hot air oven, the mechanisms of microbial inactivation would still be by coagulation of intracellular proteins. However, heat transfer from hot air is much slower than heat transfer from steam, which is why this is not seen as a practical process. Microwave irradiation could be an alternative means of sterilizing aqueous pharmaceutical products utilizing the same antimicrobial mechanisms as steam certainly there is evidence that microwave killing patterns are mainly due to heat transfer with very little direct energy being absorbed from the microwaves. 

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