ISSN:
1573-5028
Keywords:
Avena sativa L.
;
avenacosidase
;
β-glucosidases
;
BGA family
;
defence system
;
phytochrome
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract A protein consisting of 60 kDa subunits (As-P60) was isolated from etiolated oat seedlings (Avena sativa L.) and characterized as avenacosidase, a β-glucosidase that belongs to a preformed defence system of oat against fungal infection. The enzyme is highly aggregated; it consists of 300–350 kDa aggregates and multimers thereof. Dissociation by freezing/thawing leads to complete loss of enzyme activity. The specificity of the enzyme was investigated with para-nitrophenyl derivatives which serve as substrates, in decreasing order β-fucoside, β-glucoside, β-galactoside, β-xyloside. The corresponding orthonitrophenyl glycosides are less well accepted. No hydrolysis was found with α-glycosides and β-thioglucoside. An anti-As-P60 antiserum was prepared and used for isolation of a cDNA clone coding for As-P60. A presequence of 55 amino acid residues was deduced from comparison of the cDNA sequence with the N-terminal sequence determined by Edman degradation of the mature protein. The presequence has the characteristics of a stroma-directing signal peptide; localization of As-P60 in plastids of oat seedlings was confirmed by western blotting. The amino acid sequence revealed significant homology (〉39% sequence identity) to β-glucosidases that are constituents of a defence mechanism in dicotyledonous plants. 34% sequence identity was even found with mammalian and bacterial β-glucosidases of the BGA family. Avenacosidase extends the occurrence of this family of β-glucosidases to monocotyledonous plants.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00028858
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