Abstract:
:The keto form of oxaloacetate (OAA), a product of phosphoenolpyruvate carboxylase (PEPC) activity, can undergo various nonenzymatic conversions which make conventional methods of assaying the enzyme difficult, because the products may either act as inhibitors or go undetected. In studies with PEPC isolated from leaves of maize, an assay coupled with reduction of OAA to malate was compared with product analysis using high-performance liquid chromatography and an assay based on Pi release. The results show that activity of the enzyme in the assay coupled to malate dehydrogenase is underestimated, to varying extents, depending on magnesium concentration, buffer, and pH. In the assay coupled to malate dehydrogenase, inaccuracies occur due to conversion of the keto form of OAA to the enol form, which is not utilized as a substrate, and due to loss of OAA by decarboxylation to pyruvate. The assay based on Pi formation is considered to give the true rate of catalysis. With this assay the pH optimum is 7.8, compared to 8.3-8.5 for the assay coupled to malate dehydrogenase. The metal enol complex of oxaloacetate (M-OAAenol) is an inhibitor of PEPC and conditions which are favorable for forming this tautomer, high pH with divalent metal ions or high concentrations of Tris buffer at a pH below its pKa value, limit catalysis. Glycine stimulates enzyme activity, and it may have its effect by preventing the formation of the hydrated M-OAAenol complex and maintaining more of the OAA in the keto form. This interpretation is consistent with glycine stimulation of malate synthesis in the assay of PEPC coupled to malate dehydrogenase, with glycine stimulation of the decarboxylation of OAA, and with a reduction in the level of the M-OAAenol complex in the presence of glycine.
journal_name
Arch Biochem Biophysjournal_title
Archives of biochemistry and biophysicsauthors
Walker GH,Ku MS,Edwards GEdoi
10.1016/0003-9861(86)90502-3subject
Has Abstractpub_date
1986-08-01 00:00:00pages
489-501issue
2eissn
0003-9861issn
1096-0384pii
0003-9861(86)90502-3journal_volume
248pub_type
杂志文章abstract::Although an elastolytic activity in eosinophil-rich cell fractions from mice has been reported, this enzyme has not been purified and characterized as yet in any mammalian species. Eosinophilic elastase was isolated from human eosinophil fragments (cytosomes) obtained from normal and eosinophilic subjects. The enzyme ...
journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
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journal_title:Archives of biochemistry and biophysics
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journal_title:Archives of biochemistry and biophysics
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
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更新日期:2004-09-01 00:00:00
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
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pub_type: 杂志文章
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更新日期:1998-09-01 00:00:00
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pub_type: 杂志文章
doi:10.1016/j.abb.2007.12.004
更新日期:2008-03-01 00:00:00
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doi:10.1006/abbi.1999.1555
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journal_title:Archives of biochemistry and biophysics
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pub_type: 杂志文章
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pub_type: 杂志文章,评审
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
doi:10.1006/abbi.2000.1706
更新日期:2000-05-01 00:00:00
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
doi:10.1006/abbi.1998.0691
更新日期:1998-06-15 00:00:00
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
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更新日期:1992-04-01 00:00:00
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
doi:10.1016/j.abb.2007.01.005
更新日期:2007-03-15 00:00:00
abstract::A radioimmunoassay was developed to assess the response of testicular HO-1 to agents known to increase the microsomal heme oxygenase activity. Treatment of rats with human chorionic gonadotropin (hCG) increased the microsomal heme oxygenase activity in rat testis. The following data suggest that the increase was speci...
journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
doi:10.1016/0003-9861(89)90569-9
更新日期:1989-01-01 00:00:00
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journal_title:Archives of biochemistry and biophysics
pub_type: 杂志文章
doi:10.1006/abbi.1996.0360
更新日期:1996-09-01 00:00:00