The Specificity of Yeast Fatty‐Acid Synthetase with Respect to the “Priming” Substrate

Abstract

Yeast fatty acid synthetase catalyzes the synthesis of palmityl-CoA and stearyl-CoA from acetyl-CoA and malonyl-CoA. Acetyl-CoA serves as "primer" of the reaction cycle. The specificity of the fatty acid synthetase with respect to the "priming" substrate was studied on the purified enzyme.1. I n its function as primer acetyl-CoA was replaced by homologous saturated acyl-CoA derivatives (butyryl-CoA, capronyl-CoA, etc.). I n these experiments nonanoyl-CoA and d ecanoylCoA were good primers in low concentration range. This kind of fatty acid synthesis leads to normal end products.2. At higher concentrations of priming substrate an inhibitory effect became apparent with all long-chain acyl-CoA derivatives. With decanoyl-CoA the degree of inhibition was dependent on the concentration of malonyl-CoA. This was interpreted as competition between decaiioyl-CoA and malonyl-CoA.3. The rate of synthesis with ~~-3-hydroxydecanoyl-CoA and A2-decenoyl-CoA as prtmer was 25-50 times slower than with decanoyl-CoA. The rate-limiting step was the transfer of the acyl residue from CoA to the enzyme. The saturated acids C,,-C,s were isolated as end prcsducts of this synthesis.4. Derivatives of deoanoyl-CoA with ciubstitutions a t positions more distant from the Icarboxyl group were not so strongly depressed i n their priming activity, e.g. d3-decenoyl-CoA or 4-0x0-decanoyl-CoA. I n these cases the functional groups were retained during chain elongation. As reaction products unsaturated acids or 0x0 acids respectively were isolated.5. The enzymatic reduction of the double bond (A3-decenoyl-CoA) or the 0x0 grou11 (4-0x0-decanoyl-CoA) could be demonstrated only as a slow side reaction.

Engineering fungal de novo fatty acid synthesis for short chain fatty acid production

“…1b). As the MPT domain has been shown to broadly accept acyl chains of various chain lengths30, we engineered MPT for reduced malonyl affinity. As a rationale behind this mutation, a disfavoured malonyl uptake was anticipated to favour the competing release of incompletely elongated short acyl chains.…”

Fatty Acid Biosynthesis: Chain‐Length Regulation and Control

“…For off‐loading, the mature acyl chain is transferred in the “reverse” direction from the ACP to free CoA. The MPT domain has been characterized as tolerant in the transfer of acyl moieties of a broad variety of lengths, as well as in the transfer of functionalized CoA esters . In this property, it is similar to the MAT of domain of animal type I FAS.…”

Structure and function of eukaryotic fatty acid synthases

“…The binding of the palmitoyl product to the active site of MPT also coordinates the MPT-dependent elongation and AT-dependent priming reactions by facilitating the uptake of an acetyl moiety at the moment of termination : While malonyl uptake is prevented due to the blocked MPT active site, ACP can be charged with a new primer at the AT (Engeser et al 1979). It should still be noted that the MPT does not measure the length of the acyl chain in a strict sense : The MPT is able to transfer saturated acyl chains of different chain lengths readily if they are offered as CoA-bound substrates, and these acyl chains can even be fed into the reaction cycle as efficient primers (Pirson et al 1973 ;Schweizer et al 1970). In addition, if the supply of substrates is limited, the formation of saturated acyl-CoA products with shorter chain lengths is promoted in the yeast FAS complex (Sumper et al 1969).…”