Methanol lignin from Eucalyptus regnans F. Muell. and its purification by countercurrent distribution.

activated the p-nitrophenyl acetateand p-nitrophenyl butyrate-hydrolysing activity of sheep serum at a significantly slower rate than it did the paraoxon-hydrolysing activity. From this and supporting evidence involving theKm for hydrolysis activity of sheep, rabbit and hog sera and of purified paraoxonase towards p-nitrophenyl acetate, it was concluded that a new esterase hydrolysing pnitrophenyl acetate, but not paraoxon, existed in sheep and probably in hog serum. The esterase was called D-esterase. 5. Evidence was presented which suggested that D-esterase was not identical with the phenyl acetate-hydrolysing arylesterase or with the Cesterase of hog kidney. 6. The effect of manganese and the decrease in the dii8opropyl phosphorofluoridate-hydrolysing to paraoxon-hydrolysing rate from 1-8 in serum to 0-4 in purified paraoxonase preparations suggested the presence in sheep serum of a dii8opropyl phosphorofluoridatase similar to that of hog kidney, in addition to paraoxonase. 7. The paraoxonase in sheep serum was responsible for most of the tabun hydrolysis. 8. Sheep-serum and purified paraoxonase preparations hydrolysed m-nitrophenyl acetate more rapidly than they hydrolysed p-nitrophenyl acetate, and o-nitrophenyl acetate was hydrolysed least rapidly. 9. Purified paraoxonase did not hydrolyse tetraethyl pyrophosphate. The generous help and advice of Dr E. C. Webb, who saw the paper through its revisions and proof reading, is gratefully acknowledged. REFERENCES