If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
Synonyms: stearic acid biosynthesis
|Superclasses:||Biosynthesis → Fatty Acid and Lipid Biosynthesis → Fatty Acid Biosynthesis → Stearate Biosynthesis|
Pathway Summary from MetaCyc:
Stearate is a saturated fatty acid that occurs in many animal and vegetable fats and oils. It is an important constituent of milk fats, lard, and cocoa and shea butters. Stearate was first described by Michel Eugene Chevreul in 1823, and its name comes from Greek for "hard fat", reflecting the fact that stearate forms a waxy solid [Sampath05].
De novo plant fatty acid synthesis occurs primarily in plastids and chloroplasts (it was shown that at least in Arabidopsis fatty acid synthesis also occurs in the mitochondria). The process involves a series of reactions catalyzed by fatty acid synthase (FAS) complexes that provoke the condensation of a malonyl-[acp] and an acyl-[acyl-carrier protein] (see fatty acid elongation -- saturated).
In animals the last [acp]-bound intermediate appears to be a palmitoyl-[acp], and elongation to stearate proceeds via CoA-bound intermediates in the ER (see stearate biosynthesis I (animals)). In bacteria and plants elongation to stearate appears to continue via [acp]-bound intermediates, and a stearoyl-[acp] has been detected in many species [Jaworski74]. At least in plants, the elongation from a palmitoyl-[acp] to a stearoyl-[acp] is catalyzed by a dedicated β-ketoacyl-[acp] synthase, encoded by KASII (The enzyme involved in de novo fatty acid synthesis system up to a palmitoyl-[acp] is encoded by KASI) [Jaworski74a, Voelker01].
Strearoyl-[acp] can be hydrolyzed by acyl-ACP thioesterase enzymes, in which case the free fatty acids are exported to the cytosol [Jones95]. A second route involves acyl-ACP desaturase enzymes, which introduce a double bond in the 9 position of a stearoyl-[acp] to generate an oleoyl-[acp] (see oleate biosynthesis I (plants)). Since the activity of the desaturase enzymes in plants is often very high, oleate is often the main product of intraplastidial fatty acid synthesis [Harwood96].
Pathway Evidence Glyph:
Key to pathway glyph edge colors:
An enzyme catalyzing this reaction is present in this organism
An enzyme catalyzing this reaction was identified in this organism by the Pathway Hole Filler
No enzyme catalyzing this reaction has been identified in this organism
The reaction and any enzyme that catalyzes it (if one has been identified) is unique to this pathway
Jaworski74: Jaworski JG, Stumpf PK (1974). "Fat metabolism in higher plants. Properties of a soluble stearyl-acyl carrier protein desaturase from maturing Carthamus tinctorius." Arch Biochem Biophys 162(1);158-65. PMID: 4831331
Jaworski74a: Jaworski JG, Goldschmidt EE, Stumpf PK (1974). "Fat metabolism in higher plants. Properties of the palmityl acyl carrier protein: stearyl acyl carrier protein elongation system in maturing safflower seed extracts." Arch Biochem Biophys 163(2);769-76. PMID: 4153356
Rubio06: Rubio S, Larson TR, Gonzalez-Guzman M, Alejandro S, Graham IA, Serrano R, Rodriguez PL (2006). "An Arabidopsis mutant impaired in coenzyme A biosynthesis is sugar dependent for seedling establishment." Plant Physiol 140(3);830-43. PMID: 16415216
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