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Unusual AMP‐deaminase solubilization from teleost fish white muscle

A previous study described an unusual influence of neutral salts on the behavior of trout muscle AMP‐deaminase (AMPD) in its interactions with subcellular particulate matter (Lushchak and Storey 1994, Fish Physiol. Biochem. 13: 356‐368). The present study shows that this behavior is also shared by the muscle enzyme of two other fish species, sea scorpion (Scorpaena porcus) and corb (Sciena umbra), indicating that this describes a principle for AMPD interaction with cellular particulate material. AMPD binding to particulate matter increased with increasing KC1 concentration through the physiological range (100‐200 mM), but at higher salt concentrations the amount of bound enzyme was reduced. The pattern of binding was not influenced by hydrophobic interactions since addition of the nonionic detergents, Triton X‐100 or Tween‐80, did not alter the distribution of bound versus free enzyme although both detergents, at low concentrations, enhanced enzyme maximal activity. AMPD binding to particulate matter was also influenced by pH, the amount of free enzyme rising by nearly 3‐fold as pH fell within the physiological range from 7.5 to 6.5. It is concluded that neither electrostatic nor hydrophobic forrces alone can account for the unusual solubilization of AMPD from fish muscle and it is possible that the effect is also related to ion‐induced conforlnational changes in the structure of AMPD and/or of the myosin to which the enzyme binds.