eng Oriental Scientific Publishing Company Biomedical and Pharmacology Journal 0974-6242 2026-06-10 19 2 72230 article Rinad Sleman Aldhali 1 Medhat Rehan 2 Imen Ben Abdelmalek 1 Biology Department, College of Science, Qassim University, Burydah, Saudi Arabia, Department of Plant Production, College of Agriculture and Food, Qassim University, Buraydah, Saudi Arabia Streptomyces tricolor HM10 was investigated for extracellular protease and protease inhibitor production, partial purification, biochemical characterization, and gene-level confirmation. ISP-4 medium was the most suitable for production, with maximum protease inhibitor activity observed after 2 days of incubation. Casein significantly enhanced enzyme production, indicating its role as an inducer. Gel filtration chromatography on Sephacryl S-200 successfully separated protease and inhibitor activities, confirming their distinct molecular nature. The protease showed optimal activity at pH 9.0 and 50 °C, while the inhibitor exhibited maximum activity at neutral pH and 60 °C. Both biomolecules demonstrated broad pH and thermal stability. Metal ions such as Mn²⁺ and Co²⁺ enhanced activity, whereas Hg²⁺ strongly inhibited both proteins. PMSF sensitivity confirmed the serine nature of the protease. The enzyme retained stability in the presence of non-ionic surfactants, suggesting potential industrial applicability. Additionally, strong antifungal activity was observed against plant pathogens, particularly Fusarium oxysporum. PCR amplification confirmed the presence of genes encoding serine protease, subtilase-type inhibitor, and CPBP metalloprotease, while one inhibitor gene was not detected. Overall, S. tricolor HM10 represents a promising source of thermostable alkaline protease and bioactive inhibitor with potential applications in biotechnology and biocontrol. https://biomedpharmajournal.org/vol19no2/screening-partial-purification-biochemical-and-molecular-characterization-of-streptomyces-tricolor-hm10-serine-protease-and-protease-inhibitors/ Characterization Enzyme inhibitor Gene amplification Serine proteinase Streptomyces