Molecular cloning and characterization of a cDNA encoding alpha-glucosidase from spinach

A cDNA encoding spinach alpha-glucosidase was cloned and sequenced by the reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) methods. The cDNA comprised 2867 bp, and included an open reading frame which encodes a polypeptide of 903 amino acid residues. The calculated molecular mass of 101 kDa was larger than those of native alpha-glucosidases in spinach seeds, which are 78, 78, 82, and 82 kDa by SDS-PAGE for alpha-glucosidase I, II, III, and IV, respectively. The deduced amino acid sequence included those of tryptic peptides from native enzymes. Southern blot analysis suggested that the alpha-glucosidase gene was a single-copy gene. These results indicate the possibility that the multiplicity of alpha-glucosidase in spinach occurs via post-translational modification.