A novel extracellular hydrolase of similar to 45 kDa molecular mass was purified from Kluyveromyces marxianus IFO 0288 cultures and characterized as serine protease. The K-m-value of protease (designated protease-KM-IFO-0288-A), which was found active in media containing elevated [NaCl] but lacking EDTAK(2), decreased with increasing [Ca2+]. The protease maintained considerable activity at the range of 10-60 degrees C and pH 6.00-10.25, with optimum k(cat)/K-m-value at 35.5 degrees C and pH 7.75. It was strongly affected by specific irreversible inhibitors of serine proteases while was unaffected by inhibitors of cysteine proteases. Significant rate constants, activation energies, and proton inventories were estimated from the profiles of Michaelis-Menten parameters, versus pH, temperature and deuterium atom fraction, in the hydrolysis of Suc-AAPF-pNA showing that protease-KM-IFO-0288-A performs catalysis via a charge-relay system. The properties of protease-KM-IFO-0288-A suggest that K. marxianus represents a valuable source of extracellular protease of biotechnological interest which, given its GRAS status, could find several important applications. (C) 2012 Elsevier Ltd. All rights reserved.