The lipids of fish. 3. The acetone-insoluble fraction of an acetone extract of the flesh of the haddock

It can be separated from the aromatic esterase and is further distinguished from it by its sensitivity to toxic organophosphorus compounds.5. Phenyl esters are thus hydrolysed by at least five esterases in human blood: erythrocyte aceto- cholinesterase, plasma butyro-cholinesterase, ery- throcyte ali-esterase, erythrocyte aromatic esterase and plasma aromatic esterase.The last two enzymes are either identical or closely similar.We are greatly indebted to Dr W. N. Aldridge for com- municating to us the results of his work prior to publication and for helpful discussions.We are also grateful to the Medical Research Council and Hoffmann-La Roche Inc. for grants.