1. Changes in the activities of ATP citrate lyase, ;malic' enzyme, glucose 6-phosphate dehydrogenase, pyruvate kinase and fructose 1,6-diphosphatase, and in the ability to incorporate [1-(14)C]acetate into lipid have been measured in the livers of developing rats between late foetal life and maturity. 2. In male rats the activities of those systems directly or indirectly concerned in lipogenesis (acetate incorporation into lipid, ATP citrate lyase and glucose 6-phosphate dehydrogenase) fall after birth and are maintained at a low value until weaning. After weaning these activities rise to a maximum between 30 and 40 days and then decline, reaching adult values at about 60 days. ;Malic' enzyme activity follows a similar course, except that none could be detected in the foetal liver. Pyruvate kinase activity is lower in foetal than in adult livers and rises to slightly higher than the adult value in the post-weaning period. Fructose 1,6-diphosphatase activity rises from a very low foetal value to reach a maximum at about 10 days but falls rapidly after weaning to reach adult values at about 30 days. 3. Weaning rats on to a high-fat diet caused the low activities of acetate incorporation, ATP citrate lyase, glucose 6-phosphate dehydrogenase and pyruvate kinase, characteristic of the suckling period, to persist. ;Malic' enzyme and fructose 1,6-diphosphatase activities were not altered appreciably. 4. No differences could be detected in hepatic enzyme activities between males and females up to 35 days, but after this time female rats gave higher values for acetate incorporation, glucose 6-phosphate dehydrogenase activity and ;malic' enzyme activity. 5. The results are discussed in relation to changes in alimentation and hormonal influences.

1. The highest blood concentrations of ketone bodies were found at 5 days of age, after which time the concentration fell to reach the adult value by 30 days of age. 2. Both mitochondrial and cytoplasmic hydroxymethylglutaryl-CoA synthase activities were detected, with highest activities being found in the mitochondria at all stages of development. Activity of the mitochondrial enzyme increases rapidly immediately after birth, showing a maximum at 15 days of age, thereafter falling to adult values. The cytoplasmic enzyme, on the other hand, increased steadily in activity after birth to reach a maximum at 40 days of age, after which time activity fell to adult values. 3. Both mitochondrial and cytoplasmic aceto-acetyl-CoA thiolase activities were detected, with the mitochondrial enzyme having considerably higher activities at all stages of development. The developmental patterns for both enzymes were very similar to those for the corresponding hydroxymethylglutaryl-CoA synthases. 4. The activity of heart acetoacetyl-CoA transferase remains constant from late foetal life until the end of the suckling period, after which time there is a gradual threefold increase in activity to reach the adult values. The activity of brain 3-oxo acid CoA-transferase increases steadily after birth, reaching a maximum at 30 days of age, thereafter decreasing to adult values, which are similar to foetal activities. Although at all stages of development the specific activity of the heart enzyme is higher than that of brain, the total enzymic capacity of the brain is higher than that of the heart during the suckling period.

It has been reported by Hess, Haeckel & Brand (1966) that yeast pyruvate kinase (ATP-pyruvate phosphotransferase, EC 2.7.1.40) is stimulated by FDP.* This is apparently not a general property of pyruvate kinases, since in tests on extracts from Lactobacillu8 fermentii and several animal tissues stimulation by FDP was detected only with the enzyme from bovine heart muscle. Stimulation of rat-liverpyruvate kinase by very low concentrations ofFDP is now reported, the pattern ofthe kinetics of stimulation supporting the view that this is an allosteric effect.Preparation of enzyme extract. Rat liver was homogenized with 5vol. of cold distilled water in a Waring Blendor and the homogenate centrifuged at 15 000g for 1 hr. (MSE 18 centrifuge, 6 x 250 head, 12000 rev./min.). The protein of the supernatant fluid was fractionated by differential ammonium sulphate precipitation in the cold. The fraction precipitated by between 30% and 40% saturation with anmmonium sulphate, which contained 50% of the total liver pyruvate-kinase activity, was redissolved in a small volume of water and stored at 4°. Crude extracts prepared in this way had a specific activity of about 1 unit/mg. of protein and were used without further purification (1 unit is defined as 1,umole of substrate utilized/ min. at 250).As8ay. Pyruvate kinase was assayed by the method of Bucher & Pfleiderer, (1955). The reaction is coupled with lactate dehydrogenase to give oxidation of NADH2, which is followed by measuring the change in E340. Except where modified for a particular purpose the final reaction mixture contained: triethanolamine buffer, pH 7.5, 40mM; KCI, 70mM; NADH2, 0-15mM; ADP, 1-OMn; MgSO4, 8-0mM; lactate dehydrogenase [rabbit-muscle enzyme; Boehringer Corporation (London) Ltd., London, W.5], lOunits. The reaction, carried out at 250, was started with PEP.Result8. The factors governing stimulation of pyruvate kinase by FDP are complex, the stimulated/unstimulated activity ratio, which may be as high as 40, depending not only on the FDP concentration but also on PEP concentration and pH. The interrelationship between FDP and PEP is best illustrated by the data showing the influence of each of these on the velocity-concentration curve for the other. In the absence of FDP the curve for initial velocity against PEP concentration is sigmoidal (Fig. 1), the plot of l/v against 1/8 curves upwards, the Hill plot gives a maximum slope of approximately 2 and half-maximal activity is attained at 0n6mm-PEP. In the presence of high concentrations of FDP (0-5mm), the response to PEP concentration is transformed to give a Michaelis-Menten curve. The reciprocal plot is now linear, the Hill plot has a slope of 1 and the half-maximal concentration of PEP is 60,uM, i.e. tenfold lower than in the absence of FDP.The data for the converse relationship (varying FDP concentration at fixed concentrations of PEP) are less reliable, since by reason of the saturation characteristics of the system the most infornative portions of the curves occur at low reaction rates and very...

20-Oxo-steroids, in presence of a t-alkoxide in the corresponding alcohol, react with oxygen to give the 17a-hydroperoxy-20-ketone in fair yield; reduction, best with zinc and acetic acid, then gives the 17a-hydroxy-20-ketone. The speed of hydroperoxidation is notably affected by the nature of the substituents at C(,,j and in ring c. In the same way, a 6-oxo-5a-steroid is converted, via the fia-hydroperoxy-derivative, into the 5a-hydroxy-6-ketone. 3-0xo-5a-and 12-oxo-steroids, on the other hand, are oxidised to the 2 3and 11,12-dioxo-compounds respectively.KETONES react rather sluggishly with oxygen, and the products are usually those resulting from cleavage of the carbon chain adjacent to the carbonyl group; the a-hydroperoxyketone has been postulated as an intermediate, and such a compound has been isolated, along with its decomposition products, from the oxidation of di-isopropyl ketone at However, when a ketone forms a stable enol, the latter (but not the ketonic form), in solution in ether, light petroleum, or benzene, reacts readily with oxygen at ordinary temperature to give the a-hydroperoxy-ketone, which, under these mild conditions, is easily isolated ; 4*5 even secondary a-hydroperoxy-ketones have been prepared in this way, in spite of the ease with which they are dehydrated to a-diketones6Most simple ketones exist to a negligible extent in their enolic forms under neutral conditions, but enolisation is favoured by basic or acidic conditions. However, although several workers have shown that, in strongly basic medium, ketones w i l l take up oxygen rapidly at ordinary temperature, they have, again, usually isolated cleavage products ; this is readily explained by the initial formation of the a-hydroperoxy-ketone, for such compounds are known to be cleaved by base.' That autoxidation of ketones can proceed without cleavage of the carbon chain is indicated by the conversion of +unsaturated ketones of the cyperone series into their y-hydroxy-derivatives by oxygenation in presence of aqueous base8 and by the recent observation that certain rotenone derivatives give a-ketols under similar conditions? It seems probable that the hydroperoxy-ketones are intermediates in such oxidations, since there are analogies for the " reduction " of such compounds to the ketols by dilute alkali.u*c More important, for the present purpose, was the observation that, even under strongly basic conditions, the reaction can leave the carbon chain intact. Thus, cyclic ketones of type (I), in the limonin series, react with oxygen in presence of potassium t-butoxide in