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Biomedical subjects

E Roets

Publications and source records attributed to E Roets.

At least 127 records · Page 7Linked to original sources
PubMed1983

Metabolism of leucine by the isolated perfused goat udder.

Seven lactating goat mammary glands from 6 goats were perfused for several hours in the presence of [U-14C]L-leucine (4 experiments) or [2-3H; 1-14C]DL-leucine (3 experiments) and received adequate quantities of glucose, acetate and amino acids. Radioactivity in casein was mainly recovered in leucine and 90% of casein leucine was derived from free plasma leucine. About 64% of the leucine molecules were used for casein synthesis. Up to 12% of the molecules were channelled into lipid synthesis, while the remaining (up to 24%) were metabolized to CO2. From the 3H/14C ratio of casein and casein leucine, it was calculated that 70-80% of the leucine molecules were reversibly transaminated before their incorporation into milk protein. However, only 4-8% of the plasma leucine molecules were transaminated during passage through the udder. Different pools for oxidation and for protein synthesis may be present in the goat mammary gland.

Amino Acids↗
PubMed1983

Propionate for fatty acid synthesis by the mammary gland of the lactating goat.

Isolated mammary glands of lactating goats were perfused with heparinized and oxygenated blood for 8 to 15 h. Adequate quantities of glucose, acetate, and amino acid were added to the perfusate. After addition of propionate to the perfusion blood, concentrations of odd-numbered and of monomethyl-substituted fatty acids other than those with iso and anteiso configuration increased in the milk fat. These acids seem to be synthesized de novo in the mammary gland. The increase of C17:0 concentration was weak and problematic. We suggest that propionate is acting as a precursor for monomethyl-substituted fatty acids by way of methylmalonyl-CoA. The activating effect of propionate administration upon milk fatty acid production was largest for odd-numbered followed by monomethyl-substituted fatty acids. No increase of iso acids was observed in milk fat in the propionate-infused glands whereas the increase of anteiso acids was extremely small. This agrees with the conception that iso and anteiso fatty acids are synthesized by rumen bacteria.

Animals↗
PubMed1981

Effect of atropine on plasma amino acid levels and milk secretion of cows.

Subcutaneous injections of 30 mg atropine into lactating cows induced a 20--40% decrease of free amino acid (AA) levels in arterial plasma. Minimum levels were observed after 30--50 min. The decline persisted for more than 6 h. The greatest fall in concentration was noted for tyrosine, methionine, lysine, arginine, phenylalanine and threonine. Arterial glucose levels remained unaffected. The effect of atropine on milk secretion was studied in 2 cows which were milked every hour with the aid of oxytocin. Maximal effects were observed after 3--4 h. They included reduction in concentration of casein and alpha-lactalbumin (alpha-la) and a decline in production of milk (20%), casein (35%), alpha-la (45%) and lactose (18%). Uptake by the lactating udder over a period of about 1 h after injection of atropine was studied in 2 cows. Mammary blood flow and glucose uptake remained unaffected. There was a positive correlation between arteriovenous differences of essential AA and arterial plasma concentrations. The uptake of essential AA decreased by approximately 50%. There was no evidence that atropine has a direct inhibiting effect on the udder. It is suggested that the decrease of alpha-la synthesis might induce an inhibition of lactose synthesis and milk production.

Amino Acids↗
PubMed1979

Metabolism of [U-14C; 2,3-3H]-L-valine by the isolated perfused goat udder.

Two lactating mammary glands excised from 2 goats were perfused for several hours in the presence of [U-14C; 2,3-3H]-L-valine and received adequate quantities of glucose, acetate and amino acids. In the synthesized milk 96 and 89% respectively of the casein valine was derived from free plasma valine. Valine was extensively catabolized by mammary tissue, resulting in a considerable 14CO2 production and in the incorporation of 14C into milk citric acid and to a lesser extent into casein aspartic acid and glutamic acid. About 30% of the valine molecules which were taken up by the mammary gland were oxidized to CO2 and 70% were incorporated in casein as valine residues. About 10% of the plasma valine molecules were reversibly transaminated during one passage through the udder. An important amount of radioactivity of plasma was present in unknown metabolites. Only 7% of this activity was localized in isobutyrate. The radioactivity of total milk fat was very low. Mainly iso-14:0, iso-16:0 and 15:0 were labelled.

Animals↗
PubMed1979

Metabolism of ornithine in perfused goat udder.

Four lactating goat mammary glands were perfused for several hours in the presence of ornithine labeled with 1-carbon-14 and delta-nitrogen-15 or 5-hydrogen-3 and received adequate quantities of glucose, acetate, and amino acids. For the first label carbon and nitrogen were incorporated in casein of milk. After isolation of the casein amino acids the carbon-14 was incorporated into proline only while nitrogen-15 was localized in aspartic acid, glutamic acid, alanine, serine, glycine, and the branched-chain amino acids. In the experiments with hydrogen-3 labeled ornithine, no reversible transamination of ornithine could be measured during passage through the udder. After incubation in vitro of goat blood in the presence of the labeled ornithine, no nitrogen-15 could be detected in other free amino acids of plasma. Ornithine is transaminated by the udder itself. The delta-amino group of ornithine contributed nitrogen for the synthesis of several nonessential amino acids in the mammary gland.

Amination↗
PubMed1978

Substrate specificity of penicillin acylase of E. coli.

The hydrolysis of several phenylacetylamino compounds was studied using a purified preparation of E. coli penicillin acylase. The L-isomers of phenylacetyl amino acids were cleaved much faster than the D-isomers. The same observations was made for some phenylacetylamino beta-lactams. When the beta-lactam ring is incorporated in a penam or cephem ring system, the D-isomers were hydrolysed somewhat faster than the L-isomers. We also confirmed that benzylpenicillins with an hydroxy- or an amino-group in alpha-position of the side chain were hydrolysed, both in the normal and the 6-epi-series.

Amidohydrolases↗
PubMed1977

Preparation of 6-epi-ampicillin and of 6-epi-alpha-hydroxybenzylpenicillin.

The preparation of 6-epi-ampicillin by hydrolysis of 6-epihetacillin is described. During this conversion, the formation of a diketopiperazine was also observed. The best yield was obtained at pH 7.0 and room temperature for 3 approximately 7 hours. The lowest yield of 6-epi-ampicillin and the highest formation of the diketopiperazine occurred in pyridine - acetic acid - water. Treatment of ampicillin (with D-aminophenylacetyl side chain) with nitrous acid gave alpha-hydroxybenzylpenicillin with about 66% of L- and 34% mandelyl side chain. Reaction 6-epi-ampicillin gave 6-epi-alpha-hydroxybenzylpenicillin with practically the same ratio of L- and D-isomers.

Ampicillin↗
PubMed1974

Metabolism of (14C)citrulline in the perfused sheep and goat udder.

1. A lactating-sheep mammary gland was perfused for 12h in the presence of l-[2-(14)C]-citrulline and received adequate quantities of glucose, acetate and amino acids. Two lactating-goat udders were similarly perfused in the presence of either l-[carbamoyl-(14)C,-2-(14)C]citrulline or l-[carbamoyl-(14)C,1-(14)C]citrulline and l-[4-(3)H]arginine. 2. In these experiments, [(14)C]citrulline was substantially oxidized to CO(2) and converted into arginine and proline of casein. 3. The specific radioactivities of arginine, ornithine and proline of the plasma increased after passage through the udders, demonstrating that [(14)C]citrulline is metabolized by the mammary gland. 4. The presence of two unknown radioactive metabolites of [(14)C]citrulline was detected in the perfusate. These substances were not found after incubation in vitro of oxygenated blood in the presence of the radioactive precursor. 5. From these experiments, it is concluded that citrulline is metabolized in mammary tissue by way of arginine to urea, ornithine and proline.

Animals↗