4.C.2 The Carnitine O-Acyl Transferase (CrAT) Family Peroxisomes
metabolize a variety of lipids, acting as a chain-shortening
system that produces acyl-CoAs of varying chain lengths,
including acetyl-CoA and propionyl-CoA. Peroxisomes contain
carnitine acetyltransferase (CRAT) and carnitine
octanoyltransferase (CROT) that produce carnitine esters for
transport out of peroxisomes, together with recently
characterized acyl-CoA thioesterases (ACOTs) that produce free
fatty acids. Westin et al. (2008) performed tissue expression
profiling of the short- and medium-chain carnitine
acyltransferases Crat, Crot and the short- and medium-chain
thioesterases (Acot12) and (Acot5). They provided evidence that
these enzymes are largely expressed in different tissues and do
not compete for the same substrates. Rather, they provide
complementary systems for transport of metabolites across the
peroxisomal membrane. This may explain earlier observed tissue
differences in peroxisomal production of acetyl-CoA/acetyl-
carnitine/ac