DFPase As Part Of The Advanced Catalytic Enzyme System

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Introduction to Enzymes in General: Enzymes are made of protein and act as biological catalysts (by increasing the rate of reactions in organisms without themselves being affected). They lower the activation energy for chemical reactions in living organisms, which allows the reactions to occur at lower temperatures and higher speeds. Allowing the reactions to occur at lower temperatures is necessary because otherwise some reactions would need to happen at temperatures which are too high for the organism's body to handle, because proteins in it would be denatured or destroyed. The reactions also need to occur faster because many metabolic reactions naturally occur so slowly that the progress of the reaction is barely noticeable. Therefore life could not exist without enzymes. Another reason why enzymes are important to study is that they have roles in almost every metabolic reaction. The names of enzymes end in -ase (for example protease).

All enzymes are globular proteins, meaning they have specific 3D shapes and are soluble because of the hydrophilic (attracted to water) side chains on the outside of the enzyme molecules. The active site of an enzyme is like a cavity which can combine substrates to increase their ability to react with each other. A substrate is a reactant in a chemical reaction catalyzed by an enzyme. Sometimes there will be only one substrate, and the enzyme will break it down into products.

Enzyme-catalyzed reactions start out quickly, when the number of substrates is high and there is a high probability of collisions between the enzymes and the substrates, but slow down when more substrates have already been turned into product. Some factors which affect the rate of enzyme-controlled reactions include enzyme and substrate concentration, pH, temperature, cofactors, and inhibitors.

Cofactors are molecules which some enzymes need to properly catalyze reactions. They include prosthetic groups, coenzymes, and coactivators. Inhibitors are molecules which prevent an enzyme from acting as a catalyst. This can be a reversible or irreversible process. It can happen when a molecule shaped like a substrate (a competitive inhibitor) blocks the enzymes active site, or when a molecule attaches itself to another part of the enzyme which distorts the active site of the enzyme (the molecule acts as a non-competitive inhibitor). (3)

Introduction to Enzymes used in Industry: Enzymes are useful for industry because of their ability to speed up reactions and reduce the amount of energy required for a reaction. They also have potential of being used more extensively in the future because at the moment fewer than 200 enzymes are being used while about 2500 have been discovered. Also, scientists hope that they will be able to design man-made enzymes in the future to catalyze more reactions. (5). Some examples of how enzymes are used in industry are to tenderize meat (papain is used), to make cheese or yogurt (lipase is used, along with others), or as the active ingredients of biological detergents, which work because enzymes break down stains in clothes. A protease could be used to break down the proteins in blood into amino acids so that a blood stain on an item of clothing would disappear. (4).

Specific Enzyme Chosen: DFPase, which is used in the Advanced Catalytic Enzyme System (ACES) . (2) It is also sometimes called Dpase and is part of the family of hydrolases. (6).

Molecular Structure of DFPase:

The primary amino acid sequence in DFPase is very complicated but a diagram of it is shown above. For the secondary structure there are two amino acid chains, A and B. (7). The tertiary and quaternary stuctures of DFPase are also complicated and cannot be explained in words, but are shown in the image below. Calcium ions at the active site are important to its function as a catalyst for the reaction it catalyzes. (8).

Function of DFPase: The reaction between diisopropyl fluorophosphates and water, which yields diisopropyl phosphate and fluoride, and is a reversible process, is catalysed by DFPase.

Cofactors, Inhibitors: DFPase has only one cofactor called divalent cation. Chelating agent is an inhibitor of DFPase (it is uncertain whether or not there are other inhibitors of DFPase). (6).

Organism that Originally Produced DFPase: This enzyme was originally found in a type of squid (Loligo vulgaris). (2).

Use of DFPase in Industry: DFPase is used mainly in conjunction with OPH (Organophosphorus Hydrolase) and OPAA (Organophosphorus Acid Anhydrolase) ACES. (2) The enzymes in ACES are used by the US government to detoxify dangerous chemicals which terrorists would try to use in biological weapons. This can be used to protect the general public or used by the military to "clean up" areas that have been attacked with chemical weapons. ACES helps to do this quickly, which is important because soldiers wearing Chemical protection suits are less mobile and their combat abilities can be increased if they are able to remove the suits soon after the attack. (1) ACES has fire-fighting abilities (although this is due to the firefighting foams such as FireChoke or ColdFire added, not as a result of DFPase). In medicine, tests have been performed which show that adding one of the enzymes in ACES (OPAA) into a mouse's bloodstream increases its chances of surviving a nerve gas attack. Other ideas for how to use decontaminant enzymes would be for removing pesticides from harvested agricultural products, or for cleaning out the containers and equipment used for spreading pesticides over fields. (2).

How ACES is Used: ACES is a dry powder whose producers intended it to be able to be used mixed with any type of foam system (for example foams used in extinguishing flames such as FireChoke) that is now being used. The user will be able to decide whichever he prefers or which is most suitable to the task at hand. For the military, ACES can be carried by individual soldiers in small packets which weigh only one ounce, or in large barrel-type systems which fit to pumps (to spread the detoxifying material). ACES could even be sprayed out of showerheads to detoxify the chemical protection suits of people who have been working in dangerous areas before they are removed. (2).

Production (and Modifications) of ACES: A powdered version of the enzymes OPH and OPAA is obtained by a process called lyophilization and is done with a special type of sugar called trehalose sugar. DFPase is extracted from the squid where it was originally produced by a company called Biocatalytics. Modifications include adding FireChoke and ammonium carbonate, mixing all the materials together and adding water to the mixture of enzymes and other substances before they are used. (1).

Problems with the use of ACES: One substance that is difficult for ACES to detoxify is sulfur mustard, which is a dangerous chemical. This is because sulfur mustard is insoluble in water, making it difficult for ACES to work on, since ACES is used in an aqueous state. An idea to solve this would be to use organic solvents in high concentrations to dissolve the sulfur mustard, but this would require a lot of solvent and would make it difficult to carry around the decontaminant. Another method of making sulfur mustard safe is to oxidize it to mustard sulfoxide. With this process there is a danger of oxidizing the sulfur mustard enough that it becomes sulfone which is another hazardous chemical. (2).

Economical Importance of ACES: Because ACES is does not corrode metals like some other decontaminants, it saves money when whatever is being decontaminated does not need to be rinsed afterwards. As an example, an M1A1 Abrams tank needs 80 gallons (about 303liters!) of water to be rinsed thoroughly after applying Decontaminant Solution 2 (which is a corrosive decontaminant), and with ACES this need is eliminated. (2).