Abstract
Ornithine decarboxylase (EC 4.1.1. 17) is the first and the
rate-controlling
enzyme in polyamine biosynthesis. It decarboxylates L-ornithine to form diamine
putrescine. ODC activity in cells is strictly regulated and one of the central
elements of ODC regulation is an inhibitory protein called antizyme. Antizyme
binds to ODC, inhibits its activity and targets ODC for the proteasomal
degradation. Essentiality of polyamines for the normal cell growth and
proliferation is well known. Recently their roles in the regulation of several
classes of cation channels have been discovered. Some of these channels are
expressed abundantly in the brain, which has increased interest in the polyamine
metabolism in the central nervous system.
In this study guanosine 5'-triphosphate activatable ODC was detected in the
rat
brain lysates. This activation was more significant after antizyme was separated
from ODC. GTP-activatable ODC was more resistant to heat and displayed higher
Vmax than kidney ODC. Previously GTP-activatable ODC had
been found in mammalian tissues only in some tumors. ODC and antizyme expression
in brain was localized by in situ hybridization and
immunocytochemistry. Both proteins displayed wide and largely overlapping
expression patterns restricted to neurons. The proteins were localized
predominantly to cytoplasm at the most brain regions, but antizyme had a main
localization in nuclei in some regions of the brain. In addition, the role of one
of the most highly conserved regions in eukaryotic ODCs was studied using
site-directed mutagenesis. The aspartate-233 to valine mutation was made and
detected to increase Km values for the cofactor PLP and
the substrate L-ornithine as well as Ki value for the
inhibitor DFMO.
In another part of this study a transgenic mouse line expressing ODC under the
control of viral promotor was generated. The most significant changes in ODC
activity were detected in reproductive organs of male mice. The high number of
infertile transgenic males supported earlier reports about the importance of
balanced polyamine metabolism for spermatogenesis. Infertility of female mice was
increased as well, but the involvement of polyamines remained unproven.
Transgenic mice were prone to various pathological conditions such as
inflammations and tumour formation, which may be due to deregulated polyamine
metabolism.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn951-42-6631-5 |
| Date | 25 March 2002 |
| Creators | Kilpeläinen, P. (Pekka) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 2002 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/0355-3221, info:eu-repo/semantics/altIdentifier/eissn/1796-2234 |
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