Dehydrated reconstituted

Figure 1.7 Typical zero-order and corresponding second-derivative electronic absorption spectra of ethanol-reconstituted lipid/chloroform extracts of autoxidized model polyunsaturated fatty-acid compounds and inflammatory synovial fluid obtained after (1) reduction with NaBH4 and (2) dehydration with alcoholic H2S04- (a) Methyl linoleate subsequent to autoxidation in air at ambient temperature for a period of 72 h (—), or exposure to a Fenton reaction system containing EDTA (5.75 x 10 mol/dm ), H2O2 (1.14 X 10 mol/dm ) and Fe(ll) (5.75 x IO mol/dm ) as an aqueous suspension (—) (b) as (a) but with methyl linolenate (c) untreated rheumatoid knee-joint synovial fluid.

The resultant dehydrated enzyme preparations often display comparable activity to untreated enzyme when reconstituted in aqueous buffer. However, in the case of many enzymes, activity in a suitable neat organic solvent can be three to five orders of magnitude lower than in water. This was recognized by Klibanov early on in the... 

Ancient chuno production produced the first dehydrated potatoes, but for a modem context we need to move forward to the end of the 18th century. The first European reference (Burton, 1989) to dried potato was by Parmentier in France in 1781 in the form of biscuits made from boiled potatoes for use by sailors. He also discussed methods of drying cooked potatoes in forms to be reconstituted by the addition of boiling water. Although the first US patent for dehydrating mashed potatoes was granted to Edwards in 1845 (Eskew, 1959), it was in wartime in industrialized countries in the 20th century that dehydration was widely practiced. Dehydrated potatoes provided combatant troops with a food that was less bulky than fresh potatoes and easier... 

Dehydrated irradiated vegetables will absorb water much more rapidly than the nonirradiated product. This process may have great promise for use in manufactured products, such as dried soups, where rapid reconstitution is highly desirable. 

Rehydration or reconstitution is the restoration of a dehydrated food product to its original edible condition by the simple addition of water, usually just prior to consumption or further processing. 

The unsaturated residues Dha and Dhb are formed by dehydration of serine and threonine residues, respectively, and the thioether linkages Lan and MeLan are generated by intramolecular Michael-type addition of cysteine thiols to the unsaturated sites (e.g., Fig. 3b). These modifications can be performed by either two separate enzymes (LanB and LanC) in class I lantibiotics or a single bifunctional enzyme (LanM) in class II lantibiotics. Typically, proteolysis of the leader sequence is performed by a dedicated protease, either a LanP serine protease (class I) or the cysteine protease domain of a LanT protein (class II). The lanB genes encode large ( 1000 residues) predominantly hydrophilic dehydratases that may be membrane associated. To date, the dehydratase activity of a LanB protein has not been reconstituted in vitro and little is known about the mechanism of catalysis of this group of enzymes. 

The lanC genes encode smaller ( 400 residues), zinc met-alloproteins that catalyze cysteine thiol addition to unsaturated amino acids to form the lanthionine and methyllanthione residues in a regioselective, stereoselective, and chemoselective manner (Fig. 3b). The first experimental evidence for the role of LanC proteins in lantibiotic biosynthesis was the accumulation of dehydrated NisA in strains that lack the NisC protein (14). In 2006, the crystal structure of NisC was solved, and its cyclase activity was reconstituted in vitro (15). Its active site contains a single zinc atom with one histidine and two cysteine... 

After dehydration, the OH groups can be reconstituted by exposure to water at elevated temperatures. This is illustrated by the spectra in Figure 2 for CeY and SmY. Except for a small change in frequency of the high-intensity OH band, the spectra are similar. After evacuation at 427°C, 2 mm of water pressure is placed on the sample and an immediate increase in OH band intensities is observed. This is particularly true for the 3630 and the 3500 cm" bands. Upon lowering to 260°C, a further increase in intensity occurs however, some physically adsorbed water is also present at these conditions, as indicated by a band near 1635 cm" (not shown). 

The abbreviation DRV stands for Dehydration-Rehydration Vesicles as initially named by the inventors of this liposome preparation technique (1). However, one will find several other explanations in the relevant literature as Dried Rehydrated Vesicles and Dried Reconstituted Vesicles, which are actually the same type of liposomes. 

Salinas, J.P et al., Lipid derived aroma compounds in cooked potatoes and reconstituted dehydrated potato granules, in Lipids in Food Flavors, Ho, C.T. and Hartman, T.G., Eds., American Chemical Society, Washington, D.C., 1994, p. 108. 

Based on these studies in microstructure and the mechanism of moisture removal on dehydration and moisture absorption during reconstitution, good quality dehydrated products which reconstitute well upon dehydration should have the following characteristics cells must not be totally collapsed, cell walls must remain intact and intercellular spaces must be maintained in the dried product. The latter will allow capillary action to draw the water into the vicinity of the cells during the process of rehydration. Water can then diffuse across the intact cell wall and into the cells to reestablish turgor. 

R. Altman was the first to report microscopic investigations of freeze-dried tissue in 1890. Arrhenius, and later Becquerel, proposed that life originated by freeze-dried organisms that arrived on this planet from outer space and then were reconstituted by water. Becquerel calculated that if a dehydrated organism could live for one year at 10 C, then it could live for 70 billion years at -270 °C, the temperature of outer space. 

The reaction catalyzed by CDP-6-deoxy-D- /) rfro-L-t rw-4-hexulose-3-dehydrase is a further example of how the amazing versatility of vitamin Bg-derived cofactors has been exploited by nature. It is the only known example to date of a dehydration reaction catalyzed by a PMP-dependent protein. Ei depends on a [2Fe-2S] cluster for its activity. Ej is part of the 3,6-dideoxyhexoses synthetic pathway in bacteria." ° In Yersinia pseudotuberculosis Ei catalyzes the C3 deoxygenation of CDP-6-deoxy-D-g/)/r6T( -L-t) rw-4-hexulose in the biosynthetic pathway of L-ascarylose. The reducing power needed to reconstitute the active form of Ej (e.g., regeneration of PMP) is released by an enzyme of the flavodoxin-NADP reductase family, CDP-6-deoxy-D-g f6T( -L-S r6 ti-4-hexulose-3-dehydrase reductase... 

Perhaps the most appealing example of a hydration-dehydration molecular system is that of an ionic channel across a low dielectric lipid bilayer or cell membrane. With reconstitution methods, it is possible to observe one molecular channel or conducting unit at a time that is, to see the protein switching between open and closed states. 

It is hoped that such studies of single hemichannels will be complemented by studies of reconstituted junctional channels the double-membrane form. Development of a stable, well-characterized, and well-controlled double-membrane system is a challenging prospect. The literature on osmotic control of fusion of apposed bulged bilayers may be helpful in this regard (120, 121). Such a system would permit exploration of the forces involved in the assembly of junctional channels, which would be of interest from biophysical and cellular perspectives. For example, does the space between two membranes need to be dehydrated for hemichannels to interact (122) Do the hemichannels find each other by random interactions or does dielectric attraction (123-125) play a role Once junctional channels are formed, how reversible is the interaction between them and what forces tend to stabilize it Most important, how are the permeability, gating, and modulation of single hemichannels altered by interactions with each other in the doublemembrane form These and other considerations make the exploration of connexin channels in reconstituted systems of profound interest and promising prospects. 

This type of equilibrium is supported by the known details of the dehydration of hydrogen Y and the reconstitution of ammonium Y zeolite. The decrease in frequencies with increasing temperature is probably an indication of the increasing interaction between neighboring atoms in the structure. The situation is not completely clear since if the proton is visualized as moving from oxygen to oxygen atom, the lifetime... 

---