In order to reduce the protein content of wastewater, photosynthetic bacteria producing proteinases were screened from wastewater of various sources and stocked in culture. An isolated strain, KDDS1, was identified as Rubrivivax gelatinosus, a purple nonsulfur bacterium that secretes proteinase under micro-aerobic conditions under light at 35 C. Molecular weight of the purified enzyme was estimated to be 32.5 kDa. The enzyme showed the highest activity at 45 C and pH 9.6, and the activity was completely inhibited by phenylmethyl sulfonyl fluoride (PMSF), but not by EDTA. The amino-terminal 24 amino acid sequence of the enzyme showed about 50% identity to those of serine proteinases from Pseudoalteromonas piscicida strain O-7 and Burkholderia pseudomallei. Thus, the enzyme from Rvi. gelatinosus KDDS1 was thought to be a serine-type proteinase. This was the first serine proteinase characterized from photosynthetic bacteria.
An alkaline serine-proteinase from Bacillus sp. PN51 isolated from bat feces collected in Phang Nga, Thailand, was purified and characterized. The molecular mass was estimated to be 35.0 kDa. The N-terminal 25 amino acid sequence was about 70% identical with that of Natrialba magadii halolysin-like extracellular serine protease. The enzyme showed the highest proteinase activity at 60 degrees C at pH 10.0. The activity was strongly inhibited by PMSF and chymostatin. The proteinase activity was not affected by the presence of 2% urea, 2% H(2)O(2), 12% SDS, 15% triton X-100, or 15% tween 80. The proteinase preferred Met, Leu, Phe, and Tyr residues at the P(1) position, in descending order. The k(cat), K(m) and k(cat)/K(m) values for Z-Val-Lys-Met-MCA were 16.8+/-0.14 min(-1), 5.1+/-0.28 microM, and 3.3+/-0.28 microM(-1) min(-1) respectively. This is the first report of an alkaline serine-proteinase with extremely high stability against detergents such as SDS.
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