Characterization of the isozymes of glucuronoxylan xylanohydrolase in the presence of a native cell wall substrate.
A simple but accurate method for measuring glucuronoxylan xylanohydrolase activity was developed using coleoptile cell wall particles prepared from maize (Zea mays L.). Two isozymes of glucuronoxylan xylanohydrolases designated as GX1 and GX2 (EC 3.2.1.136) were purified from a commercially available amylase preparation to electrophoretic homogeneity by three cation exchange chromatography steps. Upon characterization no significant differences between the two enzymes were detected: the molecular mass measured by MALDITOF mass spectrometry was 44,360 +/- 100 for GX1 and 44,370 +/- 50 for GX2 suggesting no difference in the total number of amino acid residues. Furthermore the N-terminal amino acid sequence for each of the isozymes was identical through the 37th amino acid residue. The values of pI were determined to be 9.0 for GX1 and 9.1 for GX2. The sensitivity to temperature, pH and to ionic strength was similar for both isozymes as were kinetic parameters including Km and Vmax. No differences could be detected in substrate specificity.
Hayashi
K
K
Department of Vegetable Crops, University of California, Davis, USA.
Inouhe
M
M
Aoyagi
C
C
Nevins
D J
DJ
D000595:Amino Acid Sequence; D002473:Cell Wall / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007527:Isoenzymes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009994:Osmolar Concentration; D017421:Sequence Analysis; D013696:Temperature; D014995:Xylosidases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D003313:Zea mays
D007527:Isoenzymes; D014995:Xylosidases; C068045:glucuronoxylan xylanohydrolase