Ascorbate peroxidase. A prominent membrane protein in oilseed glyoxysomes.
The glyoxysomes of growing oilseed seedlings produce H2O2, a reactive oxygen species, during the beta-oxidation of lipids stored in the cotyledons. An expression library of dark-grown cotton (Gossypium hirsutm L.) cotyledons was screened with antibodies that recognized a 31-kD glyoxysomal membrane polypeptide. A full-length cDNA clone (1258 bp) was isolated that encodes a 32-kD subunit of ascorbate peroxidase (APX) with a single, putative membrane-spanning region near the C-terminal end of the polypeptide. Internal amino acid sequence analysis of the cotton 31-kD polypeptide verified that this clone encoded this protein. This enzyme, designated gmAPX, was immunocytochemically and enzymatically localized to the glyoxysomal membrane in cotton cotyledons. The activity of monodehydroascorbate reductase, a protein that reduces monodehydroascorbate to ascorbate with NADH, also was detected in these membranes. The co-localization of gmAPX and monodehydroascorbate reductase within the glyoxysomal membrane likely reflects an essential pathway for scavenging reactive oxygen species and also provides a mechanism to regenerate NAD+ for the continued operation of the glyoxylate cycle and beta-oxidation of fatty acids. Immunological cross-reactivity of 30- to 32-kD proteins in glyoxysomal membranes of cucumber, sunflower, castor bean, and cotton indicate that gmAPX is common among oilseed species.
Bunkelmann
J R
JR
Graduate Program in Molecular and Cellular Biology, Arizona State University, Tempe 85287-1601, USA.
Trelease
R N
RN
D000595:Amino Acid Sequence; D060387:Ascorbate Peroxidases; D001483:Base Sequence; D002458:Cell Fractionation; D003488:Cyanogen Bromide; D017931:DNA Primers; D018076:DNA, Complementary; D015151:Immunoblotting; D008565:Membrane Proteins / Q000032:analysis / Q000096:biosynthesis* / Q000737:chemistry; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D015388:Organelles / Q000201:enzymology* / Q000648:ultrastructure; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D010544:Peroxidases / Q000032:analysis / Q000096:biosynthesis* / Q000737:chemistry; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D018076:DNA, Complementary; D008565:Membrane Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D010544:Peroxidases; D060387:Ascorbate Peroxidases; D003488:Cyanogen Bromide