Short-chain fatty acids -3-hydroxybutyric acid

Ruminant milk fats contain a high level of butanoic add (C4 0) and other short-chain fatty acids. The method of expressing the results in Table 3.6 (%, w/w) under-represents the proportion of short-chain adds-if expressed as mol %, butanoic acid represents c. 10% of all fatty acids (up to 15% in some samples), i.e. there could be a butyrate residue in c. 30% of all triglyceride molecules. The high concentration of butyric (butanoic) acid in ruminant milk fats arises from the direct incorporation of jS-hydroxybutyrate (which is produced by micro-organisms in the rumen from carbohydrate and transported via the blood to the mammary gland where it is reduced to butanoic acid). Non-ruminant milk fats contain no butanoic or other short-chain adds the low concentrations of butyrate in milk fats of some monkeys and the brown bear require confirmation. 

Ketone bodies The short chain fatty acid metabolites acetoacetate and p-hydroxybutyrate and acetone. 

Kose GT, Kenar H, Hasirci N, Hasirci V (2003) Macroporous poly(3-hydroxybutyrate-co-3-hy-droxyvalerate) matrices for bone tissue engineering. Biomateiials 24 1949-1958 Kourmentza C, Ntaikou I, Kornaros M, Lyberatos G (2009) Production of PHAs from mixed and pure cultures of Pseudomonas sp. using short-chain fatty acids as carbon source under nitrogen limitation. Desalination 248 723-732... 

PHA can also be employed as an antibacterial agent against disease outbreaks. Short-chain fatty acid PHA were found to be effective in inhibiting the growth of a virulent Vibrio campbellii strain which is known to infect molluscs, finfish, lobsters and shrimp. The assumption was made that when the PHA particles degraded into P-hydroxybutyrate, fatty acids were released in the guts of Artemia nauplii. The use of smaller sized PHA particles could also improve the survival of infected Artemia nauplii more effectively [30]. In a different study conducted by Nhan and co-workers [31], Artemia nauplii were fed a lipid emulsion rich in highly unsaturated fatty acids and PHA. This technique, known as lipid enrichment, was employed... 

Ugwu CU, Tokiwa Y, Aoyagi H, Uchiyama H, Tanaka H (2008) UV mutagenesis of Cupriavidus necator for extraceliuiar production of (R)-3-hydroxybutyric add. J Appl Microbiol 105 236-242 Valentin HE, Steinbiichel A (1994) Application of enzymatically synthesized short-chain-length hydroxy fatty acid coenzyme A thioesters for assay of polyhydroxyalkanoic add biosynthesis. Appl Microbiol Biotechnol 40 699-709... 

In ruminants, / -hydroxybutyrate is the preferred chain initiator (labelled / -hydroxybutyrate appears as the terminal four carbons of short- to medium-chain acids), i.e. the first cycle in fatty acid synthesis commences at /J-hydroxybutyryl-S-ACP. 

In the ruminant mammary tissue, it appears that acetate and /3-hydroxybutyrate contribute almost equally as primers for fatty acid synthesis (Palmquist et al. 1969 Smith and McCarthy 1969 Luick and Kameoka 1966). In nonruminant mammary tissue there is a preference for butyryl-CoA over acetyl-CoA as a primer. This preference increases with the length of the fatty acid being synthesized (Lin and Kumar 1972 Smith and Abraham 1971). The primary source of carbons for elongation is malonyl-CoA synthesized from acetate. The acetate is derived from blood acetate or from catabolism of glucose and is activated to acetyl-CoA by the action of acetyl-CoA synthetase and then converted to malonyl-CoA via the action of acetyl-CoA carboxylase (Moore and Christie, 1978). Acetyl-CoA carboxylase requires biotin to function. While this pathway is the primary source of carbons for synthesis of fatty acids, there also appears to be a nonbiotin pathway for synthesis of fatty acids C4, C6, and C8 in ruminant mammary-tissue (Kumar et al. 1965 McCarthy and Smith 1972). This nonmalonyl pathway for short chain fatty acid synthesis may be a reversal of the /3-oxidation pathway (Lin and Kumar 1972). 

The de novo synthesis of fatty acids in the mammary gland utilizes mainly acetate and some (3-hydroxybutyrate. These precursors arise from the microbial fermentation of cellulose and related materials in the rumen. Once in the mammary gland, acetate is activated to acetyl-CoA. The mechanism of fatty acid synthesis essentially involves the carboxylation of acetyl-CoA to malonyl-CoA, which is then used in a step-wise chain elongation process. This leads to a series of short-chain and medium-chain length fatty acids, which differ by two CH2 groups (e.g., 4 0, 6 0, 8 0, etc.) (Hawke and Taylor, 1995). These are straight-chain, even-numbered carbon fatty acids. However, if a precursor such as propionate, valerate or isobutyrate, rather than acetate, is used, branched-chain or odd-numbered carbon fatty acids are synthesised (Jenkins, 1993 see Chapter 2). 

The fatty acids are converted to short-chain oxy acids usually called ketone bodies, such as P-hydroxybutyrate and P-ketobutyrate, which are highly water soluble and are circulated easily in the blood. The ketone bodies are efficient nutrients because they enter directly into the mitochondria for aerobic metabolism. The heart uses ketone bodies all the time. Adipose tissue surrounds the heart and even permeates into it, providing a direct and efficient energy supply for this constantly working tissue. The brain adapts to the use of ketone bodies as nutrients... 

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