2. The carbon dioxide ratio, i.e. the ratio of the specific activities of expired carbon dioxide during the infusion of [1-14C]acetate and [2-14C]acetate, respectively, was 1-58 ± 0-17 (3) for non-pregnant sheep, 1-66 ± 0-25 (4) for sheep in early pregnancy, 1-74 + 0-14 (4) for sheep in late pregnancy, and 1-18 ± 0-11 (3) for under-fed sheep in late pregnancy. Calculations based on the last two ratios indicate that citric acid-cycle turnover in under-fed pregnant sheep is about one-quarter of the turnover found in well-fed pregnant sheep.3. The output of carbon dioxide is similar in all four groups of animals, but the percentage of carbon dioxide derived from acetate is low in the poorly-fed sheep in late pregnancy. The amount of acetate converted into carbon dioxide is lower in these animals but, because total aceta.te utilization is low in this group, the acetate presented to the tissues is oxidized as readily as in the sheep of other groups.

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1. Fraction I, a fraction containing acidic glycoproteins, isolated from guinea-pig serum, was digested with Pronase after removal of sialic acid and a major and a minor glycopeptide fraction were isolated by chromatography with Sephadex G-25 and G-50. 2. The major fraction was examined by various methods and shown to contain several glycopeptides. Estimates of molecular weight of the glycopeptide fractions were obtained. Although some variation appeared to occur, the glycopeptides were not grossly heterogeneous with respect to size. An average prosthetic group was estimated to contain about 15 sugar residues. 3. Aspartic acid was the principal amino acid present in the fractions and in all subfractions of the major fraction investigated. Where examined, ammonia was liberated on acid hydrolysis in approximately equimolar amounts to the aspartic acid present. The carbohydrate composition of the fractions was also determined. 4. The glycopeptides showed relatively little degradation in alkaline solution. 5. These results suggest that an N-acylglycosylamine bond involving aspartic acid forms the major type of linkage between carbohydrate and polypeptide. The isolation of a compound with the composition and chromatographic properties of 2-acetamido-1-(l-beta-aspartamido)-1,2-dideoxy-beta-d-glucose supports this view, and indicates that N-acetylglucosamine is the sugar involved in at least many linkages. 6. Fraction I contains some glycoproteins that are susceptible to Pronase and one or more others that resist digestion before the removal of sialic acid. A brief examination revealed some similarities between prosthetic groups derived from both kinds of glycoprotein.

1963 D(-)-f-hydroxybutyrate:acetoacetate ratios reported in the present paper (Table 5) indicate that in incubated liver slices from well-fed rats the NAD:NADH2 ratio within the mitochondria is lower than in slices from starved rats. Some support for this conclusion is provided by the observation of Frunder & Richter (1955) and Kayne, Taylor & Alpert (1963) that during incubation the NAD :NADH2 ratio increases more rapidly in liver slices from starved rats or rats given a lowcarbohydrate diet than in liver slices from rats given a balanced diet.Calcium ions increase the D( -)-fl-hydroxybutyrate: acetoacetate ratio (and presumably therefore decrease the NAD: NADH2 ratio) (Table 5), but there seems to be no correlation between this effect and the effects of Ca2+ ions on total ketonebody production. SUMMARY 1. Calcium ions decrease the total amount of ketone bodies formed by liver slices from fed rats, but increase the total formed by liver slices from starved rats and rats given a low-carbohydrate diet.2. Calcium ions enhance ketone-body production by liver slices from fed and starved rats in the presence of octanoate, but the effect is more marked with starved animals. In contrast, Ca2+ ions depress the formation of ketone bodies from both fed and starved animals when pyruvate is the substrate.3. The ratio of D(-)-p-hydroxybutyrate to acetoacetate formed is increased by Ca2+ ions (about threefold); the value for the ratio is higher in liver slices from fed animals than in liver slices from starved animals. 4.

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