Incorporation of [14C]glucose into lactose and neuramin-lactose by rat mammary glands

The identity of a novel form of sialyl-lactose found in milk of the echidna (Tachyglossus aculeatus) was investigated. The sialyl-lactose yielded equimolar amounts of N-acetylneuraminic acid and lactose during mild acid hydrolysis but was resistant to the action of a bacterial neuraminidase. A viral neuraminidase hydrolysed it to lactose plus a form of sialic acid that reacted positively with thiobarbituric acid reagent but whose chromatographic mobility was greater than that of N-acetylneuraminic acid. Treatment with alkali converted the sialyl-lactose into a substance with the same chromatographic mobility as N-acetylneuraminyl-(2-->3)-lactose and made it susceptible to the action of bacterial neuraminidase. The sialyl-lactose contained one mol of ester (identified as acetyl), and released one mol of formaldehyde during periodate oxidation, per mol of sialic acid. It did not contain N-glycollylneuraminic acid. These results indicate that the sialyl-lactose is N-acetyl-4-O-acetylneuraminyl-(2-->3)-lactose. Echidna milk contained, in addition, a small amount of N-acetylneuraminyl-(2-->3)-lactose.

Section: Discussionmentioning

confidence: 99%

Identification of N-acetyl-4–O-acetylneuraminyl-lactose in echidna milk

Messer

1974

“…The situation appears similar to that of the synthesis of neuraminlactose. From enzyme experiments lactose was assumed to be the normal precursor of neuraminlactose (Jourdian, Carlson & Roseman, 1963) but after labelled glucose was given to lactating rats the rates of labelling of lactose and neuraminlactose were practically identical (Carubelli, Taha, Trucco & Caputto, 1964). An explanation for this apparent discrepancy was given by Barra, Cumar & Caputto (1969), who in experiments in vitro showed that synthesis of neuramin from free lactose must be negligible compared with that occurring when the synthesis of lactose and the subsequent binding of the sialyl group is carried out by one and the same enzyme complex.…”

Section: Time (Days)mentioning

confidence: 99%

The biosynthesis of gangliosides. Labelling of rat brain gangliosides in vivo

Maccioni

Arce²,

Caputto

1971

1. After injection of [6-(3)H]glucosamine into 8-day-old rats it was found that all the major brain gangliosides and their sialyl groups were labelled at essentially the same rate, except the hematoside, which was the least labelled. In 18-day-old rats it was found that the two major gangliosides with the sialyl (2-->8)-sialyl linkage, and their sialyl groups were more labelled than the hematoside, the Tay-Sachs ganglioside, the other two major gangliosides and their respective sialyl groups. 2. No difference was found in any of the cases studied between the specific radioactivities of the neuraminidase-resistant and -labile sialyl groups belonging to the same ganglioside. The same was found for the specific radioactivities of the galactosyl groups proximal and distal to the ceramide moiety of total brain gangliosides from rats injected with [U-(14)C]glucose. From this it was concluded that partial turnover of the ganglioside molecule does not occur. 3. A model for the synthesis of gangliosides is presented that accounts for results from previous experiments in vitro and the lack of precursor-product relationships observed in experiments in vivo.

“…In one experiment it was eluted and hydrolysed, yielding glucose and galactose. It is probably neuraminyl-lactose, described by Carubelli et al (1964). Table 2 summarizes the incorporation of glucose carbon atoms into the products, and Table 3 summarizes the distribution of individual carbon atoms (C-1, C-2, C-3 and C-6) observed in two groups of experiments.…”

Section: C-labelled Glucosementioning

confidence: 99%

Pentose cycle and reducing equivalents in rat mammary-gland slices

Katz

Wals

1972

1. Slices of mammary gland of lactating rats were incubated with glucose labelled uniformly with (14)C and in positions 1, 2, 3 and 6, and with (3)H in all six positions. Glucose carbon atoms are incorporated into CO(2), fatty acids, lipid glycerol, the glucose and galactose moieties of lactose, lactate, soluble amino acids and proteins. C-3 of glucose appears in fatty acids. The incorporation of (3)H into fatty acids is greatest from [3-(3)H]glucose. (3)H from [5-(3)H]glucose appears, apart from in lactose, nearly all in water. 2. The specific radioactivity of the galactose moiety of lactose from [1-(14)C]- and [6-(14)C]-glucose was less, and that from [2-(14)C]- and [3-(14)C]-glucose more, than that of the glucose moiety. There was no randomization of carbon atoms in the glucose moiety, but it was extensive in galactose. 3. The pentose cycle was calculated from (14)C yields in CO(2) and fatty acids, and from the degradation of galactose from [2-(14)C]glucose. A method for the quantitative determination of the contribution of the pentose cycle, from incorporation into fatty acids from [3-(14)C]glucose, is derived. The rate of the reaction catalysed by hexose 6-phosphate isomerase was calculated from the randomization pattern in galactose. 4. Of the utilized glucose, 10-20% is converted into lactose, 20-30% is metabolized via the pentose cycle and the rest is metabolized via the Embden-Meyerhof pathway. About 10-15% of the triose phosphates and pyruvate is derived via the pentose cycle. 5. The pentose cycle is sufficient to provide 80-100% of the NADPH requirement for fatty acid synthesis. 6. The formation of reducing equivalents in the cytoplasm exceeds that required for reductive biosynthesis. About half of the cytoplasmic reducing equivalents are probably transferred into mitochondria. 7. In the Appendix a concise derivation of the randomization of C-1, C-2 and C-3 as a function of the pentose cycle is described.