Assuming that (i) the percentage of dead bacteria in lake water is usually quite high and (ii) proteolytic enzymes are relatively stable, dead and metabolically inactive bacteria may constitute a huge enzymatically active platform for protein degradation processes in lake water. Owing to the methodological difficulties associated with distinguishing between enzymes attached to the surface of alive bacteria and enzymes attached to dead bacteria, <a href="http://www.selleck.cn/products/ipi-145-ink1197.html
">Duvelisib</a> it is hard to show directly which part of the total proteolytic activity in natural lake water is associated with dead bacterial cells or their fragments. Nevertheless, there are reasons to assume the widespread presence of such an activity in aquatic environments. These reasons are related to the fact that enzymes attached to dead bacteria and their fragments hydrolyze proteins and polypeptides without the coupled assimilation of amino acids (end products of catalysis). The large share of such enzymes in natural lakes can easily explain the following observations: <a href="http://www.selleckchem.com/products/byl719.html
">Alpelisib order</a> (1) the lack of a strong correlation between bacterial numbers and proteolytic activity; (2) the presence of free dissolved amino acids, even in bacteria-abundant environments, where at least theoretically, potential bacterial demand for carbon and nitrogen should be high (Kiersztyn, 2005); (3) the lack of a strong correlation between bacterial production and protease activity; and (4) the release of FAA from organic particles colonized by bacteria observed by Hoppe (1991) and Smith et?al. (1992). It is the latter observation, confirmed by the results of our 2-year investigations, which we consider especially interesting. We found a strong positive correlation (r2?=?0.70, P?��?0.008) between amino acid concentration and aminopeptidase activity in <a href="http://www.selleckchem.com/products/SB-431542.html
">SB431542 cost</a> the seston particles fraction. This result suggests that amino acids are liberated from particulate matter into the surrounding water, as was proposed by Hoppe (1991). Such a loss of FAA is disadvantageous for attached bacteria producing proteolytic enzymes, because they spend energy on enzyme synthesis but do not gain the full benefits of monomer possession, as the latter are consumed only partially. This paradoxical loss of monomers after hydrolysis is inconsistent with the idea of a ��hydrolysis-uptake coupling system�� (Fuhrman, 1987), which assumes that all monomers enzymatically liberated by bacteria are immediately assimilated by them. If we suppose that the biofilm surrounding the particles functions as a ��trap�� for dead but still enzymatically active bacteria and bacterial cell debris, the release of amino acids from the seston particles into the surrounding environment can be easily explained. The results of our experiments lead us to propose a division of the dead bacterial proteolytic enzyme pool into two fractions. The first pool ��slow but stable proteases�� includes the enzymes of free-living bacteria and those connected with small (<1.