Owing to their broad substrate specificity, plant α-type phospholipases D (PLD) are an interesting alternative for the industrial production of modified phospholipids. Nevertheless, structural information of these enzymes are still restricted. A surface model of the PLD2 from cabbage was deduced from small angle X-ray scattering data. The PLD2 is a monomeric enzyme with a longish shape, looser structered in the apical and basal regions. Calcium ions are essential for activity. The increase in activity and molar ellipticity in the near UV range at 280 nm was specifically dependent on the calcium concentration and revealed two calcium binding events with dissociation constants of 0,07 or 0,16 mM and 19,1 or 8,6 mM, respectively. Spectroscopic techniques like fluorescence and circular dichroism (CD) spectroscopy were used for the characterization of the protein. The first unfolding step of the guanidine hydrochloride (GdnHCl)- and urea-induced unfolding as well as the temperature and acidinduced unfolding of the enzyme yielded partially unfolded PLD2. This partially unfolded PLD2 bound 1-anilino-naphthalene sulfonate and had a native-like secondary structure but no distinct tertiary structure. Consequently, this intermediate showed porperties similar to the molten globule state. However, using analytical ultracentrifugation, the partially unfolded PLD2 was identified as heterogeneous aggregates. No monomeric species could be detected. The formation of the aggregates explained the irreversibility of the first unfolding step. The detected structural alteration and the enzyme inactivation coincided. The unfolding of the PLD2 secondary structure was induced by higher concentrations of GdnHCl or urea proofed by CD- and fluorescence spectroscopy. This second unfolding step was highly cooperative and reversible leading to a random coil-like conformation. As the first unfolding step was irreversible and showed only little changes in secondary structure, separate unfolding of domains causing the two unfolding steps of the denaturant-induced unfolding was precluded. In accordance with results of PLD2 enzyme fragments, the first unfolding step is interpreted as the destruction of specific domain interactions whose correct formation possibly needs co-translational folding. A folding scheme could be established which summarizes these results in connection with kinetic folding- and unfolding data.