Vitamin K1-3H (I mg; 12 PCi) was injected intravenously into three normal men, into three patients undergoing duodenal intubation and into a patient with T-tube drainage of the common bile duct. In the normal subjects lipid-soluble radioactivity (representing the injected vitamin K1-3H) disappeared rapidly from the plasma: the clearance curve for the first 6 hr could be resolved graphically into two exponential functions, the first with a T+ of 20-24 min and the second with a T+ of 121-150 min: water-soluble radioactivity, presumed to be metabolic products, appeared in the plasma within 30 min after injection, reached a peak at z hr

—Lipid‐free extracts of rat and human brain have been prepared and shown to contain phospholipase A1 and A2 activities and a lysophospholipase. The phospholipase Aj activity has pH optima of 4·2 and 4·6 in rat and human brain, respectively; it can be partially purified and isolated in high yields by dialysing the extracts at low pH. The purified preparations hydrolyse the ester bond at the 1‐position in lecithin, phosphatidyl‐ethanolamine and phosphatidylserine, but have little or no action on triglyceride or cholesterol ester. An assay system for the enzyme is described. Phospholipase A2 activity is optimal at pH 5·5 in rat brain extracts and at pH 5·0 in extracts of human brain. The phospholipase A2 activity of human cerebral cortex is largely unaffected by heating extracts at 70°C for 5 min, whereas this treatment substantially inactivates phospholipase A1 and completely destroys lysophospholipase. Phospholipase A1 is widely distributed in both grey and white matter of human brain and is also present in peripheral nerve. Phospholipase A2 activity is lower than A1 in all regions of the CNS examined so far, and is absent from peripheral nerve. Neither enzyme appears to require Ca2+ but both are inhibited by di‐isopropylfluorophosphate (DFP, 2 × 10−6 m) and thus differ from phospholipase A of pancreas. These studies confirm that the phospholipase A1 and A2 activities in brain are due to separate enzymes.

The radioactivity in the plasma, urine and faeces has been determined in three studies carried out in two normal men after an oral dose of tritiated vitamin K, (50-100 pCi). Radioactivity in the plasma was detected by 30 min, reached a peak at 2-4 hr and then declined relatively rapidly. A low level of radioactivity persisted in the plasma for at least 96 hr. Most of the radioactivity in the 297 298 M. J. Shearer, P. Barkhan and G. R. Webster synthesis of prothrombin and related clotting factors. It has been suggested (Van der Meer et al, 1968) that the vitamin-K dependent coagulation factors are synthesized in two steps: first, a polypeptide precursor of the factor is formed and then this precursor is changed into the functionally active form in a vitamin-K dependent step.Much remains to be known about the metabolism of vitamin K, in man and the work reported in this paper was aimed at obtaining information on the absorption of vitamin

Abstract— The phospholipase A1 (EC 3.1.1.32) and A2 (EC 3.1.1.4) activities of rat sciatic nerve homogenates have been studied. With phosphatidylcholine as substrate normal nerve had significant activity of both types at pH 5.0. Substantial increases occurred in nerve undergoing Wallerian degeneration after transection, beginning as early as 2 days after operation and rising to eight times normal values by the second week.

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