Unusual AMP‐deaminase solubilization from teleost fish white muscle

Abstract

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.

Regulation of 5'-adenosine monophosphate deaminase in the freeze tolerant wood frog, Rana sylvatica

“…Binding to myosin is a major regulatory feature of AMPD that has been extensively explored [ 18 - 21 , 26 , 31 ]. The amount of AMPD that was bound in wood frog muscle increased from 20% in control frogs to 35% in frozen animals suggesting that a greater association of AMPD with myofibrils benefited metabolism in frozen muscle.…”

Regulation of enzyme function in freeze-tolerance

“…AMPD removes AMP from the adenylate pool (Hancock et al, 2006), and this action can lead to either a temporary drain of AMP (with IMP accumulating) or to a more permanent change if IMP is channeled into catabolic pathways leading ultimately to uric acid excretion. In skeletal muscle, the enzyme is well-known to be key to stabilizing the AEC during high-intensity muscle work in a range of vertebrate species (Rundell et al, 1992b;Rundell et al, 1993;Lushchak and Storey, 1994;Lushchak et al, 1997;Hellsten et al, 1999;Krause and Wegener, 1996;Fishbein et al, 1993). The regulation of AMPD is complex and includes activation or inhibition by ions and metabolite effectors (Raffin, 1984;Ashby and Frieden, 1978;Merkler and Schramm, 1990), reversible binding to myosin (Rundell et al, 1992b), oligomerization (Szydlowska et al, 2004), and covalent modification (Thakkar et al, 1993).…”

“…Binding to myosin is a major regulatory feature of AMPD that has been extensively explored (Rundell et al, 1992b;Rundell et al, 1993;Lushchak and Storey, 1994;Lushchak et al, 1997;Ashby and Frieden, 1978;Rundell et al, 1992a). The amount of AMPD that was bound in wood frog muscle increased from 20% in control frogs to 35% in frozen animals suggesting that a greater association of AMPD with myofibrils benefited metabolism in frozen muscle.…”