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octane ('the dilactone') hydrolyses spontaneously and nonenzymically to (±)-muconolactone; this hydrolysis is rapid above pH 7-0. 2. At pH 6-2-6-6, where the hydrolysis rate is low, extracts of Pseudomoncas (phthalate-utilizer), P. fiuorescens (A3.12) and Nocardia do not metabolize the dilactone at a rate in excess of its rate of hydrolysis. 3. The dilactone is now considered not to be an intermediate in protocatechuate metabolism by these microorganisms. 4. Two samples of fly-dihydroxyadipic acid failed to act as precursors of 3-oxoadipate when used as substrates in the enzyme system which converts protocatechuate into P-oxoadipate. D. W. R. gratefully acknowledges the receipt of a research studentship from the

In the normal rat there exists a continuous interchange of fat between the fat depots and the liver (a ‘triglyceride cycle’). Fat is transported in the form of non-esterified fatty acids from the depots to the liver via the blood stream. In the liver it is resynthesized to tri­glyceride, complexed with protein to form lipoprotein and is secreted into the blood stream almost certainly by the endoplasmic reticulum. It has been suggested that a fatty liver may arise by an interruption of this cycle at the site of exit from the liver. This may be the result of either an inhibition in the synthesis of the protein moiety of lipoprotein or damage to the secretory mechanism. Within 2 h of carbon tetrachloride poisoning, an inhibition to both of these processes takes place, whereas with dimethylnitrosamine, inhibition of protein synthesis precedes damage to the secretory mechanism of the endoplasmic reticulum by many hours. In contrast, thioacetamide, which produces liver necrosis without the accumulation of fat, does not have any effect on the ‘triglyceride cycle’.

Work by Marinetti, Erbland & Stotz (1958) on pig-heart-cell fractions and by Macfarlane, Gray & Wheeldon (1960) on rat-liver-cell fractions have indicated that the mitochondrial and microsomal phospholipids may differ significantly in composition. In view of the results obtained by Collins (1960) and by Collins & Shotlander (1961), showing the widespread occurrence of complex amino-phospholipids, which have not been detected by other workers, it was important to examine the phospholipids in liver-cell fractions with the procedures described by Collins & Shotlander (1961).

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