Enzymatic Properties and Multifunctional Applications of a Novel Extracellular Cold-Active Alkaline Protease from Stenotrophomonas maltophilia Strain TK-4.

A cold-active alkaline protease isolated from psychrophilic Stenotrophomonas maltophilia TK-4 strain was subjected to biochemical characterization and functional evaluation for potential industrial applications. The strain was identified by 16S rRNA gene sequencing analysis. The partially purified enzyme exhibited peak activity at 10 °C and pH 10.0. It maintained 90% of its stability within the pH range of 8.0-12.0 and 96% of its stability at temperatures between 1 and 25 °C after 24 h. When exposed to metal ions such as Co²⁺, Cu²⁺, and Mn²⁺ at a concentration of 5 mM, the enzyme retained 88.6% of its activity. Sensitivity to TLCK, EDTA, PMSF, and 1,10-phenanthroline confirmed its classification as a serine metalloprotease. The enzyme also preserved up to 92% of its activity in 1-5% NaCl concentrations. Thin-layer chromatography analysis of casein hydrolysates revealed tyrosine, histidine, cysteine, and glycine as major products. When combined with 1% commercial detergent, the protease effectively removed proteinaceous stains at low temperatures, highlighting its potential as an energy-efficient cleaning agent. In addition, it demonstrated significant fibrinolytic activity by dissolving 84.21% of in vitro blood clots within 24 h. Furthermore, its ability to completely degrade the gelatin layer on waste X-ray films highlights its potential use in silver recovery. These findings underscore the enzyme's applicability in the laundry detergent, pharmaceutical, and photographic industries.