Open AccessIsolation and function of spinach leaf β-ketoacyl-[acyl-carrier-protein] synthases
Author(s) -
Takashi Shimakata,
P.K. Stumpf
Publication year - 1982
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.79.19.5808
Subject(s) - acyl carrier protein , fatty acid synthase , spinach , acyltransferase , atp synthase , acyltransferases , biochemistry , enzyme , cerulenin , substrate (aquarium) , chemistry , biology , fatty acid , stereochemistry , biosynthesis , ecology
Crude spinach leaf extract readily forms the stearoyl derivative of acyl-carrier-protein (ACP) when acetyl-ACP and malonyl-ACP are incubated together. Palmitoyl-ACP is also elongated by malonyl-ACP to stearoyl-ACP. When β-ketoacyl-ACP synthase {3-oxoacyl-[ACP] synthase; acyl-[ACP]:malonyl-[ACP]C -acyltransferase (decarboxylating), EC 2.3.1.41} is purified with decanoyl-ACP as the assay substrate, palmitoyl-ACP elongation activity is lost. When palmitoyl-ACP is the assay substrate, another protein is isolated that specifically elongates palmitoyl-ACP to β-ketostearoyl-ACP but has no activity towards decanoyl-ACP. The first protein is designated β-ketoacyl-ACP synthase I and participates in the conversion of acetyl-ACP to palmitoyl-ACP, whereas the second protein is designated β-ketoacyl-ACP synthase II, and its substrate specificity is highly restricted to myristoyl-ACP and palmitoyl-ACP. The purification of synthase II is described, and its activity is compared to synthase I. Reconstitution experiments with the highly purified nonassociated enzymes in fatty acid synthesis plus synthases I and II clearly demonstrate the roles of these two proteins in fatty acid synthesis.