The pattern and sequence of zein degradation in the endosperm of germinating maize seeds were investigated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoblotting. The proteases involved in the degradation of various zein components (α, ß and γ) were extracted with three buffer systems and partially characterized with respect to their ability to degrade various zein components. They were also investigated in vivo by germinating the seeds in the presence of protease inhibitors used singly and in combination.
Of the various zein components, γ-zein (27-kD) was the first to be degraded and its degradation was complete by the third day after germination (DAG). Beta-zeins (17- and 18-kD) began to be degraded on the second DAG, degradation being complete by the seventh day for the l7-kD polypeptide, and the fourth day for the 18-kD polypeptide. The degradation of 10-kD- zein began on the fourth DAG and was complete by the eighth day. The α-zein fraction (22-and 24-kD) was degraded beginning on the faith day and continued gradually until after the tenth day.
From the results of these studies, the arrangement of various zein fractions within the protein bodies can be deduced and this was consistent with the immunocytochemical data published by others. Gamma-zein is situated in the peripheral region of the protein bodies and could be a structural component of the protein body membrane or it may be directly anchored in the membrane. Beta-zeins are internal to γ-zein with the l0-kD in the interface between the 17-kD and γ-zein. The 10- kD zein is located between the 17-kD and α-zein or interlacing with α-zein in the protein body core. Finally, a-zeins are in the protein body core. Based on these observations the proteolysis of the protein in protein bodies of maize would start from the periphery and proceed towards their core.
The proteases involved in degradation of various zein components were synthesized de novo. The mRNAs pre-existing in dry seeds appeared to direct the synthesis of active proteases required for zein degradation at least during the initial stages of germination. Serine protease was responsible for the degradation of a- and ß-zeins while aspartic (acid) protease may play some role in ß-zein degradation. Serine and cysteine (thiol) proteases worked synergistically in γ-zein degradation. Enzymes extractable from the endosperm of germinating seeds with 0.2 M acetate buffer (pH 3.8) were able to degrade the α-, ß-, and γ-zeins in an in vito assay. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/53589 |
| Date | January 1988 |
| Creators | Mohammad, Kamaruzaman bin |
| Contributors | Genetics, Esen, Asim, Elgert, Klaus, Scheckler, Stephen E., Stetler, David A., Stout, Ernest R. |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | x, 118 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 18668798 |
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