Bacteria proteolytic

This can be a dangerous procedure due to the potential growth of food poisoning bacteria such as Staphylococcus aureus (31). This method of inoculation requites a very strict condition to assure the absence of not only bacteria associated with a health hazard but also those associated with product failure (proteolytic, greening, and gas-forming microorganisms). 

FIGURE 2.16 pH versus enzymatic activity. The activity of enzymes is very sensitive to pH. The pH optimum of an enzyme is one of its most important characteristics. Pepsin is a protein-digesting enzyme active in the gastric fluid. Trypsin is also a proteolytic enzyme, but it acts in the more alkaline milieu of the small intestine. Lysozyme digests the cell walls of bacteria it is found in tears. 

A small number of proteins, and again insulin is an example, are synthesized as pro-proteins with an additional amino acid sequence which dictates the final three-dimensional structure. In the case of proinsulin, proteolytic attack cleaves out a stretch of 35 amino acids in the middle of the molecule to generate insulin. The peptide that is removed is known as the C chain. The other chains, A and B, remain crosslinked and thus locked in a stable tertiary stiucture by the disulphide bridges formed when the molecule originally folded as proinsulin. Bacteria have no mechanism for specifically cutting out the folding sequences from pro-hormones and the way of solving this problem is described in a later section. 

The results for bacterial whole-cell analysis described here establish the utility of MALDI-FTMS for mass spectral analysis of whole-cell bacteria and (potentially) more complex single-celled organisms. The use of MALDI-measured accurate mass values combined with mass defect plots is rapid, accurate, and simpler in sample preparation then conventional liquid chromatographic methods for bacterial lipid analysis. Intact cell MALDI-FTMS bacterial lipid characterization complements the use of proteomics profiling by mass spectrometry because it relies on accurate mass measurements of chemical species that are not subject to posttranslational modification or proteolytic degradation. 

Gram-Positive or Total Bacteria. Bacillus species are the commonest bacteria in lint, raw cottons, cotton trash, and cotton dust, and may contribute to airborne levels of proteolytic enzymes, but the counts (while high) did not correlate with dust levels, and culture filtrates do not cause histamine release. 

Clarkson et al. (1986) conclude that proteolytic enzymes contribute to root lesion formation. Accordingly, Katz et al. (1987) found root cavitation with loss of matrix to occur in mild acidic solutions only in the presence of proteases. It is conceivable that the degradation of the matrix promotes the formation of a root lesion in two ways. First, the matrix forms a barrier to ionic diffusion, which is removed by degradation. Second, the degradation of the matrix yields nutrients, which may sustain the growth of cariogenic bacteria (Hojo et al., 1991). 

Any one of these pathways, or all three, result in proteolytic cleavage of a protein known as C3 convertase to produce the active form, C3b. The latter is involved in different mechanisms that kill bacteria (Figure 17.7). 

Bacteria represent a promising source for the production of industrial enzymes. Bacterial cellulases are an especialfy interesting case in point. Many thermophilic bacterial species produce cellulases that are stable and active at high temperature, resistant to proteolytic attack, and stable to mechanical and chemical denaturation. However, cellulase productivities in bacteria are notoriously low compared to other microbial sources. In this paper bacterial enzyme production systems will be discussed with a focus on comparisons of the productivities of known bacterial cellulase producers. In an attempt to draw conclusions concerning the regulation of cellulase synthesis in bacterial systems, a tentative model for regulation in Acidothennus cellulofyticus has been developed. 

On the basis of this anti-proteolytic effect of sialic acids, a hypothetical model435 for the role of sialidase in clostridial infections is shown in Scheme 4. It is considered that the bacterial enzyme releases sialic acids from cell-surface glycoproteins of the infected tissue, which thereafter can be readily attacked by proteases. This cooperation between sialidase and protease may support the spreading of the bacteria. Acylneuraminate pyruvate-lyase, also shown in this model, degrades sialic acids for energy supply, and growth, of the bacteria. 

The proteolytic activation of bioactive sequences by lactic acid bacteria has been debated recently due to the great advantage of using food-grade microorganisms to enrich foods with bioactive substances (Gobbetti et al.,... 

FIGURE 25-8 Large (Klenow) fragment of DNA polymerase I. This polymerase is widely distributed in bacteria. The Klenow fragment, produced by proteolytic treatment of the polymerase, retains the polymerization and proofreading activities of the enzyme. The Klenow fragment shown here is from the thermophilic bacterium Bacillus stearothermophilus (PDB ID 3BDP). The active site for addition of nucleotides is deep in the crevice at the far end of the bound DNA. The dark blue strand is the template. 

The proteolysis of casein by starter culture organisms is important for proper flavor and texture development in yogurt. This topic has been reviewed by Tamime and Deeth (1980) and Rasic and Kurman (1978). In a yogurt culture, Lactobacillus bulgaricus is better able to hydrolyze casein, whereas S. thermophilus has significant peptidase activity for hydrolyzing the products of initial casein breakdown. Consequently, the proteolytic activities of the two starter culture bacteria... 

Micrococci comprise approximately 78% of the nonlactic bacteria in raw milk Cheddar cheese (Alford and Frazier 1950). The proteolytic system of Micrococcus freudenreichii functions optimally at 30 °C and at a pH near neutrality (Baribo and Foster 1952). An analysis of pro-teinases present in 1-year-old Cheddar cheese indicates that micrococci may contribute to proteolytic activity (Marth 1963). Proteolytic micrococci also contribute to the ripening of surface-ripened cheeses such as brick and Camembert (Lenoir 1963 Langhus et al. 1945). Micrococcal proteases probably contribute to development of ripened cheese flavor when ripening temperatures are above 10°C (Moreno and Kosikowski 1973). This effect results from degradation of /3-casein. 

The proteolytic systems of psychrotrophic bacteria selectively attack /3- and as-caseins (Cousin and Marth 1977A), whereas whey proteins are relatively unaffected. Growth of psychrotrophic bacteria in milk results in decreased stability of casein, as measured by rennet coagulation time and heat stability (Cousin and Marth 1977B). Growth of psychrotrophs in milk also causes an increased rate of acid production by starter cultures as a result of increased quantities of readily available nitrogen compounds (Cousin and Marth 1977C.D). 

Dyachenko, P. F., Shchedushnov, E. V. and Nassib, T. G. 1970. Characteristics of proteolytic activity of thermophilic lactic acid bacteria used for cheesemaking. XVIII Int. Dairy Congr. IE, 274. 

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