Enzymes

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Enzymes

•Definition of Enzymes

•Enzymes are proteins that catalyze (i.e., increase the rates) of chemical reactions.

•In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products.

•Role of Enzymes in Pathogenicity

•Enzymes secreted by fungi are important factors of pathogenicity.

•Dermatophytes penetrate the keratinous layer of the epidermis as well as hairs and nails and cause superficial infections. Dermatophytes produce proteases and lipases which help them invade the hosts tissues.

•The enzymes disrupt the structure of protein and lipid components of lipid cell membranes and lead to the impairment of the membranes function or to their disruption.

•Plant cell walls are composed of  polysaccharides.  the pathogens secrete the degradative enzymes which degrade the cellulose and pectin by the addition of water to break the glycosidic bonds. There are many cell wall degrading enzymes such as:

1.Cellulases

2.Pectinases

3.Hemicellulases

4.Proteases

5.Lignases

6.Cutinases

•Figure 1
Structure of Plant Cell Wall

•Figure 2
The glycosidic bond is represented by the central oxygen atom, which holds the two monosaccharides

•Hydrolytic Enzymes of Candida albicans

•Candida albicans has hydrolytic enzymes which are extracellularly secreted. They may play an important role in the pathogenicity of candidosis.

• Candida albicans causes inflammatory lesions in the mucous membrane of oral cavity.

•There is study aimed to find differences in the activity of hydrolytic enzymes of Candida albicans isolated from patients with diseases of the periodontium and mucous membrane of the oral cavity.

•Of 235 patients examined:

1.31 were diagnosed with gingivitis (inflammation of gingiva)

2.38 with glossitis (inflammation of tongue)

3.28 with leukoplakia (white patch on a mucous membrane that will not rub off)

4.37 with adult periodontitis (inflammation of gingival surrounding membranes of adults) 

5.25 with juvenile periodontitis (inflammation of gingival surrounding membranes of juvenile)

6.36 stomatitis prothetica (inflammation of oral mucosa which will die and others instead)

7.40 with stomatitis atrophica (inflammation of oral mucosa which will decrease in the size).

•In 196 patients (83.4 %), fungi belonging to Candida species were detected. Among them 146 strains of Candida albicans were found. Where detection of 19 hydrolases were found.

•Factors catalyzing enzymatic
cell wall hydrolysis

1.Optimum temperature for enzymatic activity.

2.Optimum pH for enzymatic activity.

3.Presence of specific enzyme receptors on the surface of cell wall.

4.Presence of enzyme substrate abundance.

5.Secretion of enzyme extracellularly.

6.Absence of cuticle containing pectin as in plant roots

•Factors inhibiting enzymatic
cell wall hydrolysis

1.Unsuitable environmental conditions which affect enzymatic activity such as temperature (< 20 or > 42 °C) and pH (< 6 or > 8).

2.Absence of enzyme substrate.

3.Absence of specific enzyme receptors on the surface of cell wall.

4.Secretion of enzyme intracellularly.