One of the three wheat germ inhibitors of proteinase K is bifunctional and inhibits simultaneously proteinase K (or subtilisin but not enzymes of the trypsin family) and insect α-amylase. The molecular mass of this inhibitor called PKI-3 is 21 kDa, and the binding constant for proteinase K is 0.8 nM at pH 8.2, 25°C, in 1:1 molar ratio. PKI-3 was crystallized by microdialysis against 10-12% polyethylene glycol 6000, 50 mM NaH2PO4, pH 6.7. The crystals have monoclinic space group P21 with a = 42.5, b = 65.3, c = 31.5 Å, β = 110°, and diffract beyond 2.0 Å resolution. The complex proteinase K · PKI-3 was crystallized by equilibrium vapor diffusion under the same conditions. The crystals are needle-shaped and still too small for X-ray analysis. Gel electrophoresis established the composition of the crystals. © 1986.
Pal, G. P., Betzel, C., Jany, K. D., & Saenger, W. (1986). Crystallization of the bifunctional proteinase/amylase inhibitor PKI-3 and of its complex with proteinase K. FEBS Letters, 197(1–2), 111–114. https://doi.org/10.1016/0014-5793(86)80308-8