1. An 870-fold purification of glucokinase from rat liver is described which involves ammonium sulphate fractionation and the use of DEAE-Sephadex, DEAE-cellulose and polyacrylamide columns. 2. The preparation is free of any interfering enzymes and has a specific activity of 8mumoles/min./mg. of protein. 3. Glucokinase catalyses the phosphorylation of glucose, mannose and 2-deoxyglucose. 4. The enzyme is inhibited by high concentrations of glucose 6-phosphate only; ADP is an inhibitor whose effect depends on the Mg(2+) concentration. 5. The properties of glucokinase are compared briefly with those of other phosphotransferases.

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1. Magnesium ions are the most effective bivalent ions in the glucokinase reaction. 2. The molecular weight of rat hepatic glucokinase is 48000-49000 as assessed by gel filtration on Sephadex G-100. 3. Anomalous kinetic behaviour at low glucose concentrations appears to be due to the formation during the purification procedure of fragments possessing modified catalytic properties, but is unlikely to be of physiological significance. 4. Extension of previous studies (Parry & Walker, 1966) suggests that glucokinase catalyses a reaction of the random Bi Bi type similar to that of yeast hexokinase. 5. The inhibitory effects of various thiol reagents suggest that a thiol group may be involved at or near the binding site of the acceptor molecule.

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1 The effects of the thromboxane synthetase inhibitor dazoxiben (UK 37248) on arachidonic acid and collageninduced platelet aggregation and arachidonate acid metabolism were studied both in vitro and ex vivo in the presence and absence of sources of prostaglandin 12 synthetase. 2 In platelets activated by exogenous arachidonic acid, the anti-aggregatory activity of dazoxiben was weak compared with indomethacin, despite comparable inhibition of TXB2 production. This was due to the accumulation of pro-aggregatory metabolites, principally endoperoxides. 3 The anti-aggregatory activity of dazoxiben, both in vitro and ex vivo, was higher and more consistent when platelets were stimulated by collagen, threshold levels of which resulted in an endoperoxide accumulation only 2-3% of that achieved with exogenous arachidonic acid. 4 The anti-aggregatory activity of dazoxiben is enhanced if drug equilibration is facilitated by prolonging the preincubation time from 2 to 15 minutes. 5 Incubation of platelets with pig aortic microsomes, which act both as aggregant and a source of PGI2 synthetase, facilitates the conversion to PGI2 of some endoperoxides accumulated after dazoxiben, resulting in augmented anti-aggregatory activity. 6 Leukocytes as well as blood vessels have the capacity to generate PGI2 from platelet derived endoperoxides. This was demonstrated by the increases in 6-keto-PGFia accompanying decreased TXB2 production in clotted whole blood from volunteers treated with dazoxiben. 7 It was concluded that a closer approach to in vivo conditions allowing a fuller expression of the mechanism of action of dazoxiben could be achieved in vitro by stimulating platelets with a pathophysiological activator such as collagen in the presence of a source of PGI2 synthetase.