[Multiplicity of the molecular forms of acetylcholinesterase and thermal acclimatization in Carassius auratus].

Multiple forms of acetylcholinesterase have been studied in Goldfish adapted to 15 degrees C and 25 degrees C. Three forms of enzyme (sedimenting at 18S, 12S and 5S) could be distinguished by sucrose gradient centrifugation. Their molecular and enzymatic properties did not vary with environmental temperature. It was noted that the relative proportion of the three forms differed between brain and muscle extracts, the 18S forms predominating in muscle (about 75 per cent) the 12S forms being more abundant in the brain, suggesting a physiological differentiation between these forms. The latter form varied from 48 per cent to 70 per cent in Goldfish adapted to 15 degrees and 25 degrees C respectively. The relative efficiency of saline buffer solubilization for each form also depended on the tissue used and in all cases decreased with rising environmental temperature. These two facts are taken to reflect interactions between acetylcholinesterase and membrane that depend on the nature of the membrane and probably involve the aliphatic chains of its phospholipids. The greater case of solubilization found in the low temperature adapted fish may be a function of the increased fluidity of the cellular membranes formed at lower temperatures.