Structural studies on the iron storage protein, apoferritin
type: CreativeWork
description: Horse spleen apoferritin consists of 24-subunits symmetraically arranged around a central iron-containing cavity. It was originally thought that the 24 subunits were identical, however evidence based on SDS-PAGE and isoelectrofocusing led Drysdale to propose a model with two distinct subunits, the L subunit (m.wt. 19,000) and H subunit (m.wt 21,000) which are combined in different proportions to give various 24-mers (isoferritins). This model has been disputed by several workers. When horse spleen apoferritin is electrophoresed by SDS-PAGE it resolves into several bands. The origin of these bands were studied. Bands were visible with molecular weights above and below that of the subunit. Using a 2-dimensional technique several of these band could be attributed to inter-molecular disulphide bonds forming dimers and trimers and an intra-molecular disulphide bond giving an apparently smaller subunit band (m.wt. 15,000). Other smaller molecular weight bands have been re-assessed by SDS-PAGE to have molecular weights of 11,000 (peptide B) and J+, 500 (peptide C). Aminoacid analysis indicates peptide C arises from the C-terminal end of the molecule. Sequencing of this peptide gave the following sequence: leu-thr-leu-lys-aromatic-trp which corresponds to the last six amino acids of the published sequence. Peptide C could therefore extend beyond this sequence and one explanation of this could be that the H subunit is a precursor of the L subunit. A glycoprotein affinity column showed that glycosylated subunits did occur but the extent of glycosylation was insufficient to affect the subunit molecular weight on SDS-PAGE but may be sufficient to influence isoelectro-focusing profiles. Solid-phase sequencing studies carried out on isolated L and H-rich subunits showed that both were resistent to sequencing from the N-terminal end. This implies that H as well as L subunits are H-blocked. Chemical modifications, cleavage and spectrophotometric studies indicated the presence of 1 …
abstract: Horse spleen apoferritin consists of 24-subunits symmetraically arranged around a central iron-containing cavity. It was originally thought that the 24 subunits were identical, however evidence based on SDS-PAGE and isoelectrofocusing led Drysdale to propose a model with two distinct subunits, the L subunit (m.wt. 19,000) and H subunit (m.wt 21,000) which are combined in different proportions to give various 24-mers (isoferritins). This model has been disputed by several workers. When horse spleen apoferritin is electrophoresed by SDS-PAGE it resolves into several bands. The origin of these bands were studied. Bands were visible with molecular weights above and below that of the subunit. Using a 2-dimensional technique several of these band could be attributed to inter-molecular disulphide bonds forming dimers and trimers and an intra-molecular disulphide bond giving an apparently smaller subunit band (m.wt. 15,000). Other smaller molecular weight bands have been re-assessed by SDS-PAGE to have molecular weights of 11,000 (peptide B) and J+, 500 (peptide C). Aminoacid analysis indicates peptide C arises from the C-terminal end of the molecule. Sequencing of this peptide gave the following sequence: leu-thr-leu-lys-aromatic-trp which corresponds to the last six amino acids of the published sequence. Peptide C could therefore extend beyond this sequence and one explanation of this could be that the H subunit is a precursor of the L subunit. A glycoprotein affinity column showed that glycosylated subunits did occur but the extent of glycosylation was insufficient to affect the subunit molecular weight on SDS-PAGE but may be sufficient to influence isoelectro-focusing profiles. Solid-phase sequencing studies carried out on isolated L and H-rich subunits showed that both were resistent to sequencing from the N-terminal end. This implies that H as well as L subunits are H-blocked. Chemical modifications, cleavage and spectrophotometric studies indicated the presence of 1 …
author: Paterson, Margaret
language: eng
date published: 1984
date modified: 2026-07-24T00:50:16Z
provider: Abertay University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Abertay University