The utilization of methylmalonyl-CoA for branched-chain fatty-acid synthesis by preparations from bovine (Bos taurus) adipose tissue

Integrated analysis of genomics and transcriptomics revealed the genetic basis for goaty flavor formation in goat milk

Goat milk exhibits a robust and distinctive "goaty" flavor. However, the underlying genetic basis of goaty flavor remains elusive and requires further elucidation at the genomic level. Through comparative genomics analysis, we identified divergent signatures of certain proteins in goat, sheep, and cow. MMUT has undergone a goat-specific mutation in the B12 binding domain. We observed the goat FASN exhibits nonsynonymous mutations in the acyltransferase domain. Structural variations in these key proteins may enhance the capacity for synthesizing goaty flavor compounds in goat. Integrated omics analysis revealed the catabolism of branched-chain amino acids contributed to the goat milk flavor. Furthermore, we uncovered a regulatory mechanism in which the transcription factor ZNF281 suppresses the expression of the ECHDC1 gene may play a pivotal role in the accumulation of flavor substances in goat milk. These findings provide insights into the genetic basis underlying the formation of goaty flavor in goat milk. STATEMENT OF SIGNIFICANCE: Branched-chain fatty acids (BCFAs) play a crucial role in generating the distinctive "goaty" flavor of goat milk. Whether there is an underlying genetic basis associated with goaty flavor is unknown. To begin deciphering mechanisms of goat milk flavor development, we collected transcriptomic data from mammary tissue of goat, sheep, cow, and buffalo at peak lactation for cross-species transcriptome analysis and downloaded nine publicly available genomes for comparative genomic analysis. Our data indicate that the catabolic pathway of branched-chain amino acids (BCAAs) is under positive selection in the goat genome, and most genes involved in this pathway exhibit significantly higher expression levels in goat mammary tissue compared to other species, which contributes to the development of flavor in goat milk. Furthermore, we have elucidated the regulatory mechanism by which the transcription factor ZNF281 suppresses ECHDC1 gene expression, thereby exerting an important influence on the accumulation of flavor compounds in goat milk. These findings provide insights into the genetic mechanisms underlying flavor formation in goat milk and suggest further research to manipulate the flavor of animal products.

Inhibition in vitro of lipogenic enzymes from bovine (Bos taurus) mammary tissue by methylmalonyl-coenzyme A and coenzyme A

Bovine mammary fatty acid synthetase was inhibited by approximately 50% by 40 microM methylmalonyl-CoA; this inhibition was competitive with respect to malonyl-CoA (apparent Ki = 11 microM). Similarly, 6.25 microM coenzyme A inhibited the synthetase by 35% and this inhibition was again competitive (apparent Ki = 1.7 microM). Apparent Km for malonyl-CoA was 29 microM. The short-chain dicarboxylic acids malonic, methylmalonic and ethylmalonic at high concentrations (160-320 microM) and ATP (5 mM) enhanced the synthetase activity by about 50% respectively; the activating effects of methylmalonic acid and ATP on the synthetase were additive. Methylmalonyl-CoA at 50 microM concentration inhibited the partially purified acetyl-CoA carboxylase uncompetitively by 10% and the propionyl-CoA carboxylase activity of the enzyme preparation competitively (apparent Ki = 21 microM) by 40%. Malonyl-CoA also inhibited the acetyl-CoA carboxylase activity competitively (apparent Ki = 7 microM) by 35% and the propionyl-CoA carboxylating activity of the preparation competitively (apparent Ki = 4 microM) by 82%. The possibility that methylmalonyl-CoA may be a causal factor in the aetiology of the low milk-fat syndrome in high yielding dairy cows is discussed.

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.

The effect of dietary methyl branched-chain fatty acids on aspects of hepatic lipid metabolism in the rat

1. Rats were fed to appetite on a stock laboratory diet or on diets consisting of the stock diet and in addition 50 or 200 g triolein/kg, 50 g palmitic acid/kg or 50 g/kg of a concentrate mixture of methyl branched-chain fatty acids (Me-BCFA) which had been prepared from sheep adipose triacylglycerols. 2. No differences could be detected in the delta 9-desaturase activity or fatty acid synthetase activity of liver preparations from rats which had been fed on either the stock diet, the 50 g palmitic acid/kg or the 50 and 200 g triolein/kg diet; the palmitic acid diet was therefore taken as the control diet in subsequent experiments. 3. Rats consuming the 50 g Me-BCFA/kg diet exhibited a marked reduction in the capacity of their liver microsomes for delta 9-desaturation when compared with animals receiving the control diet. The delta 6-desaturase activity also showed an inhibitory trend with the Me-BCFA diet. 4. Microsomal omega-oxidation of fatty acids, mitochondrial succinate oxidation and the activity of cytosolic fatty acid synthetase (FAS) were unaffected by the ingestion of the Me-BCFA mixture compared with the diet which included palmitic acid. 5. There were no differences in the plasma concentration of thyroxin, insulin and glucagon between animals fed on the diets containing palmitic acid or the Me-BCFA. 6. For a given concentration of fatty acids the Me-BCFA had a greater inhibitory effect when added to incubations of liver microsomes from rats fed on the standard diet than did the addition of palmitic acid. 7. The observations in vivo and in vitro strongly suggested that the Me-BCFA were having a specific inhibitory effect on the desaturation reaction.

The use of clustering techniques in the elucidation or confirmation of metabolic pathways. Application to the branched-chain fatty acids present in the milk fat of lactating goats

The aim of this paper is 2-fold. (1) To propose the use of a group of mathematical techniques, called clustering, in the elucidation of complex metabolic relationships. (2) To apply clustering for the identification of related groups of saturated fatty acids having a common metabolic pathway for their biosynthesis in the milk fat of lactating goats. In this way, four groups of branched-chain fatty acids and two groups of straight-chain fatty acids are identified; the odd-numbered iso-, the even-numbered iso-, the anteiso-acids and the branched-chain fatty acids with methyl substitution in the chain, the odd-numbered straight-chain and the even-numbered straight-chain fatty acids. The long-chain fatty acids are not part of any group. The different metabolic pathways for their biosynthesis are discussed. From the results, it is concluded that clustering is indeed a potentially useful tool in the study of complex metabolic relationships.

Composition and variability of the branched-chain fatty acid fraction in the milk of goats and cows

Branched-chain fatty acids of the milk fat of goats were analyzed by high resolution gas chromatography-mass spectrometry. Iso-and anteiso-acids predominated, but a range of other monomethyl-branched components, mostly with methyl-substitution on carbons 4 and 6, was present. Analysis of the milk fat of cows revealed the presence of iso-and anteiso-fatty acid; other monomethyl-substituted fatty acids, as found in the milk fat of the goat, were virtually absent. Only a trace amount of 6-methylhexadecanoate was detected. The difference between goats and cows in the effectiveness with which these animals metabolize propionyl-CoA and methylmalonyl-CoA is discussed.

Methylmalonic acid in low-fat milk syndrome

The possible association between low-fat milk syndrome and methylmalonic acid accumulation in blood was investigated. Blood was sampled from the internal iliac artery of nine lactating dairy cows fed ad libitum roughage plus grain or high grain, restricted roughage diets. Daily milk fat percent and milk fat production were decreased 44% and 47% on the high grain, restricted roughage diet. No differences in blood methylmalonate concentrations could be detected in the cows fed the two diets. The effect of methylmalonate and its metabolic precursor, propionate, on mammary rates of fatty acid synthesis was determined with bovine mammary tissue slices. Neither of these metabolites affected acetate incorporation into fatty acids. Methylmalonate and propionate were incorporated into fatty acids at extremely low rates. Low-fat milk syndrome is not caused by accumulation of methylmalonic acid.

Mammary extraction of propionate in lactating cows

Four cows with exteriorized carotid arteries were in an intensive study of concentrations in plasma and mammary extraction of propionate. A restricted-roughage, high-grain diet produced higher arterial propionate concentrations and larger carotid-subcutaneous abdominal vein (arteriovenous) differences that the control diet. Concomitant changes in acetate, beta-hydroxybutyrate, and glucose in plasma and in fat and protein in milk were measured. Mammary arteriovenous difference in propionate was correlated negatively with milk fat percentage. However, since arterial propionate and beta-hydroxybutyrate also were correlated negatively, evidence of a direct inhibitory effect of propionate in mammary gland is equivocal.