Mazur-type OPA anhydrase

Although the primary investigation into the OPA anhydrases of squid tissue has been of the squid-type OPA anhydrase, squid does contain the more widespread "Mazur-type" OPA anhydrase. Gill, heart, mantle, and blood tissues all exhibit OPA anhydrase activities that are Mn2+-stimulated and hydrolyze soman faster than DFP (Hoskin et al. 1984). 

The multiple activities in T. thermophila share some of the characteristics of both the squid-type OPA anhydrase and classical Mazur-type OPA anhydrase found in hog kidney. In crude preparations, the OPA anhydrase activity has the characteristics of the hog kidney OPA anhydrase in that it hydrolyzes soman faster than DFP, is stimulated by Mn2+, and is inhibited by mipafox. Further purification has revealed that the hydrolysis of soman and the stimulation of this hydrolysis by Mn2+ is principally due to the Tt DFPase-4. The Tt DFPase-1, Tt DFPase-2, and Tt DFPase-3 hydrolyze soman and DFP at approximately the same rates and demonstrate only moderate stimulation of soman hydrolysis by Mn2+ and yet are inhibited by mipafox. The Tetrahymena OPA anhydrases fall within a narrow range from 96,000 Da to 67,000 Da. However, this range of molecular weights is larger than that typically ascribed to the Mazur-type enzymes. The Tetrahymena OPA anhydrases can be purified by ammonium sulfate precipitation, like the squid-type OPA anhydrase. 

Comparison of Several Aquatic OPA Anhydrase Activities with Typical Squid and Mazur-Type OPA Anhydrolases... 

Nervous tissue of a variety of invertebrates has been screened for OPA anhydrase activity. Other mollusks have been reported to contain OPA anhydrases, notably Octopus, Anisodoris (sea-lemon), Aplysia (sea-hare), and Sepia (cuttlefish) (Hoskin and Long 1972). Sepia and Octopus hydrolyze DFP faster than tabun, a squid-type OPA anhydrase characteristic employed at that time, and now by the DFP/soman ratio. Conversely, Aplysia, Spisula, andHomarus (lobster) hydrolyze tabun faster than DFP (Hoskin and Brande 1973), a typically Mazur characteristic. Soman to DFP ratios and Mn2+ stimulation for several species are shown... 

It is natural to wish to impose a classification scheme upon the OPA anhydrases that would imply a set of phylogenetic relationships. The classification scheme of squid-type and Mazur-type anhydrases has proven useful in that it was quickly possible to differentiate the squid-type OPA anhydrase from the other forms. As will be seen below, many of the OPA anhydrase activities lie somewhere in between. 

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