Doctoral Dissertations

Date of Award

3-1987

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Biochemistry and Cellular and Molecular Biology

Major Professor

Jayant G. Joshi

Committee Members

Thomas Montie

Abstract

Phytoferritin obtained from soya bean (Glycine max) was characterized and compared to horse spleen ferritin. The plant protein is present in two distinct forms, the smaller of which appears to be derived from the larger via proteolytic processing. The protein shows considerable sequence homology, as monitored by TLC peptide mapping, with both rat liver and horse spleen ferritin, although no immuno-crossreactivity could be detected. Only the larger (28 kdal.) form is present in 18 hr. soaked seeds, whereas the smaller protein (22 kdal.) becomes apparent after 72 hrs. There is a corresponding appearance of ferritin crystalline arrays after 72 hrs., suggesting the presence of a hemosiderin-1ike structure. Sucrose gradient centrifugation and native gradient gel electrophoresis indicate a loss of subunits from the small form, with a corresponding decrease in protein stability. Precise reproduction of the 22 kdal. form from the 28 kdal. form may be achieved by treatment with subtilisin, suggesting the plant may mark the ferritin for degradation by minor proteolysis.

Analysis of non-ferrous metal binding to the plant protein shows that the protein can bind Al, Be, Cd and Zn in amounts similar to the mammalian protein. Parallel experiments with synthetic iron polymers (artificial cores) indicate that the iron center of ferritin is responsible for much of this binding.

Large amounts of iron are released from the seed during the initial stages of imbibition. Along with this material is also a low-molecular weight (<1000 dal.) component with properties suggesting a sugar-amino acid conjugate. This partially purified factor is a potent chemoattractant for Rhizobia bacteria, as measured by a modification of capillary assay analysis. This factor may play an important role in bacterial recruitment for future nodulation.

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