title: A cysteine proteinase inhibitor purified from apple fruit.
abstract: A cysteine proteinase inhibitor has been purified from immature fruit of Malus domestica (var. Royal Gala). The M(r) of this apple cystatin is estimated to be 10,700 by MALDI-TOF mass spectrometry, 11 300 by SDS-PAGE and 11,000 by gel filtration. It is a relatively strong inhibitor of papain with a Ki value of 0.21 nM and also inhibits ficin and bromelain but not cathepsin B. An amino acid sequence was obtained from a peptide produced by trypsin digestion of the inhibitor. Comparison with other plant sequences shows a high degree of homology with other phytocystatins. As the single cysteine proteinase inhibitor detectable in immature apple fruit (5-8 mm diameter), levels of 83.3 pmol/g FW were determined. In larger fruit (up to 16 mm diameter) significantly less inhibitor was present (6.9 pmol/g FW). Given these low levels, it is postulated that this inhibitor has an endogenous role in apple fruit development rather than one of protection against pest or microbial attack.
authors.affiliation: Horticulture and Food Research Institute of New Zealand, Auckland, New Zealand.
authors.forename: S N
authors.initials: SN
authors.lastname: Ryan
authors.forename: W A
authors.initials: WA
authors.lastname: Laing
authors.forename: M T
authors.initials: MT
authors.lastname: McManus
mesh_terms: D000595:Amino Acid Sequence; D002846:Chromatography, Affinity; D015853:Cysteine Proteinase Inhibitors / Q000737:chemistry / Q000302:isolation & purification*; D004591:Electrophoresis, Polyacrylamide Gel; D005638:Fruit / Q000737:chemistry*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010936:Plant Extracts / Q000737:chemistry / Q000302:isolation & purification*; D019685:Rosales / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D015853:Cysteine Proteinase Inhibitors; D010936:Plant Extracts