Fatty acid binding proteins from developing human fetal brain: Characterization and binding properties.

Two fatty acid binding proteins (FABPs) of identical Mr, 13 kDa, have been isolated from developing human fetal brain. A delipidated 105,000g supernatanwt as incubated with [1 -'4C]oleate and subjectedt o a Sephacryl S-200 column followed by gel filtration chromatography on a Sephadex G-75 column and ion-exchange chromatography using a DEAE-Sephacel column. Purity was checked by UV spectroscopy, SDS-PAGE, isoelectric focusing and immunological cross-reactivity. The two FABPs designated as DE-I (pI 5.4) and DE-n (pI 6.9) showed cross-reactivity with each other and no alteration at the antigenic site during intrauterine development. Anti-human fetal brain FABP does not cross-react with purified human fetal heart, gut, lung or liver FABPs. The molecular mass of DE-I and DE-n is lower than those of fetal lung and liver FABPs. Like liver FABP, these proteins bind organic anions, fatty acids and acyl CoAs but differ in their binding affinities. Both DE-I and DE-n have been found to exhibit higher affinity for oleate (Kd = 0.23 ~M) than palmitate (Kd = 0.9 ~M) or palmitoyl-CoA (Kd = 0.96 ~M), with DE-I binding less fatty acids than DE-n. DE-II is more efficient in transferring fatty acid from phospholipid vesjcles than DE-I indicating that human fetal brain FABPs may playa significant role in fatty acid transport in developing fetal brain.

Relationship between glycerol-3-phosphate dehydrogenase, fatty acid synthase and fatty acid binding proteins in developing human placenta.

The activities of the enzymes glycerol-3-phosphate dehydrogenase and fatty acid synthase are inhibited by palmitoyl-coenzyme A and oleate. The two isoforms of fatty acid binding proteins (PI 6·9 and PI 5·4) enhance the activities of glycerol-3-phosphate dehydrogenase and fatty acid synthase in the absence of palmitoyl-coenzyme A or oleate and also protect them against palmitoyl-coenzyme A or oleate inhibition. Levels of fatty acid binding proteins, the activities of the enzymes fatty acid synthase and glycerol-3-phosphate dehydrogenase increase with gestation showing a peak at term. However, the activity of fatty acid synthase showed the same trend up to the 30th week of gestation and then declined slightly at term. With the advancement of pregnancy when more lipids are required for the developing placenta, fatty acid binding proteins supply more fatty acids and glycerol-3-phosphate for the synthesis of lipids. Thus a correlation exists between glycerol-3-phosphate dehydrogenase, fatty acid synthase and fatty acid binding proteins in developing human placenta.

Relationship between fatty acid binding proteins, acetyl-CoA formation and fatty acid synthesis in developing human placenta.

The relationship between fatty acid binding proteins, ATP citrate lyase activity and fatty acid synthesis in developing human placenta has been studied. Fatty acid binding proteins reverse the inhibitory efect of palmitoyl-CoA and oleate on ATP citrate lyase and fatty acid synthesis. In the absence of these inhibitors fatty acid binding proteins activate ATP citrate lyase and stimulate [ 1–14 C] acetate incorporation into placental fatty acids indicating binding of endogenous inhibitors by these proteins. Thus these proteins regulate the supply of acetyl-CoA as well as the synthesis of fatty acids from that substrates. As gestation proceeds and more lipids are required by the developing placenta fatty acid binding protein content, activity of ATP citrate lyase and rate of fatty acid synthesis increase indicating a cause and efect relationship between the demand of lipids and supply of precursor fatty acids during human placental development.