Functions of Double Subunits of a Type, Structure of Iron Corn, and Kinetics of Iron Release from Membrane Ferritin of Human Placenta
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As an experimental material of human placental tissue, membrane ferritin of human placenta (HPMF) with electrophoresis purity was prepared in batch. SDS-PAGE approach reveals that the protein shell consists of double subunits of a type in HPMF, which the molecular weights of both subunits were calculated to be approximately 15 and 20 kDa respectively, named MF(15) and MF(20). In addition, the protein content of MF(15) is about three times more than that of M(20) in SDS- PAGE gel. Using the approach of peptide mass fingerprinting (PMF), both MF(15) and MF(20) subunits were identified to show the high homology with reference to L subunit of human ferritin, pointing out that HPMF was a novel ferritin of two subunits involving in single type and different molecular weight. Using a matrix-assisted laser desorption ionization time of flight mass spectrometry to investigate the subunit-stability of HPMF, five mass peaks corresponding ratio (m/z) of mass to charge such as 5071. 25, 9962. 51, 15131. 55 (MF(15)), 19936. 40 (MF(20)) and 20147. 61 were indicated to have five subunit formula of [MF(15)](3+), [MF(20)](2+), [MF,](+), [MF(20)](+) and [MF(20+Fe)](+) respectively. Using inductively coupled plasma-mass spectrometry to analyze the elemental composition of HPMF, only 85 Fe(3+) and 15 inorganic phosphate (P(i)) in the iron core of per molecular of HPMF were found, which was significantly lower than that of most mammal ferritins, but higher than that of bacterial ferritin (BF). Kinetic studies showed that iron release from the complete HPMF followed the law with first-order reaction, which also differed from that with two different rates in mammal ferritins. In addition, the time of the iron release completely needed about 750 min in human placental membrane ferritin (HPMF), which was longer than 60 min in both horse spleen ferritin (HSF) and pig pancreatic ferritin (PPF). Accordingly, based on the difference of structure and function among HPMF, mammalian ferritins, plant ferritins, and BF, we proposed M(15) and M(20) subunit play different role in iron transporting from maternal blood to fetal blood.
CitationCHINESE JOURNAL OF ANALYTICAL CHEMISTRY，2011，39（2）：155-162