In this study, a milk-clotting enzyme (MCE) isolated from Paenibacillus spp. BD3526 was purified and characterized. The MCE was purified 8.9-fold with a 10.11% recovery using ammonium sulfate precipitation and anion-exchange chromatography and the specific milk-clotting activity (MCA) reached 6791.73SU/mg. The enzyme was characterized as a 35kDa metalloproteinase, and the zymogen of which was encoded by a 1671bp gene named zinc metalloproteinase precursor (zmp) with a predicted molecular weight of 59.6kDa. The optimal temperature for MCA and proteolytic activity (PA) was 65°C and 60°C, respectively. The enzyme was stable over a pH range of 5.0-9.0 and at temperatures below 50°C. The MCA was completely inactivated when the enzyme was heated at 60°C for 30min, and the PA was totally inactivated for 20 and 10min when the enzyme was heated at 55°C and 60°C, respectively. The BD3526 enzyme was preferentially active towards ?-casein (?-CN) and ß-casein (ß-CN), as determined by sodium dodecyl sulfate-polyacrylamide gels (SDS-PAGE), whereas the hydrolysis of as-casein (as-CN) was slow and comparable to that caused by chymosin and asparatic acid proteinase from Rhizomucor miehei. The cleavage site of the metalloproteinase in ?-CN was located at the Met106-Ala107 bond, as determined by mass spectrometry analysis. Copyright © 2016. Published by Elsevier B.V.
Journal: International journal of biological macromolecules