Diisopropyl fluorophosphate structure

The mammalian serine proteases have a common tertiary structure as well as a common function. The enzymes are so called because they have a uniquely reactive serine residue that reacts irreversibly with organophosphates such as diisopropyl fluorophosphate. The major pancreatic enzymes—trypsin, chymotrypsin, and elastase—are kinetically very similar, catalyzing the hydrolysis of peptides... 

The preceding experiments prove that there is an intermediate on the reaction pathway in each case, the measured rate constants for the formation and decay of the intermediate are at least as high as the value of kcat for the hydrolysis of the ester in the steady state. They do not, however, prove what the intermediate is. The evidence for covalent modification of Ser-195 of the enzyme stems from the early experiments on the irreversible inhibition of the enzyme by organo-phosphates such as diisopropyl fluorophosphate the inhibited protein was subjected to partial hydrolysis, and the peptide containing the phosphate ester was isolated and shown to be esterified on Ser-195.1516 The ultimate characterization of acylenzymes has come from x-ray diffraction studies of nonspecific acylenzymes at low pH, where they are stable (e.g., indolylacryloyl-chymotrypsin),17 and of specific acylenzymes at subzero temperatures and at low pH.18 When stable solutions of acylenzymes are restored to conditions under which they are unstable, they are found to react at the required rate. These experiments thus prove that the acylenzyme does occur on the reaction pathway. They do not rule out, however, the possibility that there are further intermediates. For example, they do not rule out an initial acylation on His-57 followed by rapid intramolecular transfer. Evidence concerning this and any other hypothetical intermediates must come from additional kinetic experiments and examination of the crystal structure of the enzyme. 

The diisopropylfluorophosphatase (DFPase) is found in cephalopod nerve, hepatopancreas and saliva from squid (Anderson et al. 1988). Structurally similar to PONl, the DFPase also is a calcium-containing hydrolase with a six-bladed p-propeUer fold and readily hydrolysis the organophosphate fluoride, diisopropyl-fluorophosphate (DFP), as well as the nerve agents sarin, soman and cyclosarin, in addition to the cyanide-containing OP, the nerve agent tabun (Fig. 3.15). DFPase was initially found to hydrolyze P-F and P-CN bonds and to be inert toward P-0 or P-S bonds (Bigley and Raushel 2013). 

Figure 13.9 The Structural Formulas of Acetylcholine and Diisopropyl Fluorophosphate.

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