Lysozyme

I.U.B.: 3.2.1.17
Mucopeptide N-acetylmuramolylhydrolas

Lysozyme (muramidase) hydrolyzes preferentially the β-1,4 glucosidic linkages between N-acetylmuramic acid and N-acetylglucosamine which occur in the mucopeptide cell wall structure of certain microorganisms, such as Micrococcus lysodeikticus. A somewhat more limited activity is exhibited towards chitin oligomers (Holler et al. 1975a and b).

Lysozyme is of widespread distribution in animals and plants. That which has been most extensively studied is from hen egg white (lysozyme "c"). A second avian egg white lysozyme is that of the domestic goose designated lysozyme "g" (Prager et al. 1974). Lysozyme is also found in mammalian secretions and tissues, saliva, tears, milk, cervical mucus, leucocytes, kidneys, etc.

Human lysozyme from urine has been crystallized by Osserman (1967) and extensively investigated (Osserman et al. 1974). It has been indicated (Osserman et al. 1973) that lysozyme may be the mediator in the anti-tumor function of macrophages which, it has been shown, secrete the enzyme (Gordon et al. 1974). See also Asdourian et al. (1975). There is evidence that cartilage lysozyme has a role in cartilage calcification (Kuettner et al. 1974).

There has been interest in lysozyme as a "natural" antibiotic and as an aid in the diagnosis of disease ( Glynn 1968; Pruzanski and Saito 1969). Elevated levels of serum and urinary lysozyme are present in monocytic and mono-myelocytic leukemia (Osserman and Lawlor 1966; Brierre et al. 1974). Presence of the enzyme in cerebrospinal fluid is indicative of tumor of the central nervous system (Newman et al. 1974). Hankiewicz and Swiervzek (1974) report that normally lysozyme activity is practically absent from urine, bile and spinal fluid.

Plant lysozyme is found in ficus and papya latex, and chemically is distinct from the egg white enzyme (Meyer et al. 1946). Jollés and Jollés (1975) have reported on lysozyme from Asterias rubens. A polypeptide with lysozyme activity has been synthesized (Sharp et al. 1973).

The enzyme has been used for lysing E. coli and Streptomycetes for extraction purposes (Haas and Dowding 1975) such as extracting group specific antigen (Watson et al. 1975). It would appear that lysozyme may act as a germinative agent of bacterial spores (Ando 1975; Duncan et al. 1972).

Considerable physicochemical information is available for lysozyme. Structure-function relationships are thoroughly reviewed by Imoto et al. (1972) and Phillips (1972). Jollés (1969) and Chipman and Sharon (1969) have provided descriptions of the enzyme and its catalytic mechanism.

Characteristics of Lysozyme from Chicken Egg White:

Molecular weight: 14,388 (Jollés 1969).

Composition: Amino acid sequence is reported by Jollés et al. (1963) and Canfield (1963). Tertiary structure is treated comprehensively by Imoto et al. (1972) and Warme and Scheraga (1974). Other reports on molecular properties are by Baldo et al. (1975), Formoso and Forster (1975), Halford (1975), Hsi and Bryant (1975), Kuramitsu et al. (1975), Atkinson and Bruice (1974), Bertiou and Jollés (1974), Holler et al. (1974), and Matthyssens and Kanarek (1974). Atassi et al. (1974) describe the binding site as a cleft across one side of the molecule that can accommodate six b(1--->4) less linked units of 2-acetamido-2-deoxy-D-glucopyranose.

Optimum pH: 9.2 (Davies et al. 1969).

Extinction coefficient: = 26.4 (Aune and Tanford 1969).

Isoelectric point: pH 11.0 (Alderton et al. 1945).

Specificity: Egg white and comparative lysozyme specificities are described by Hara and Matsushima (1967 and 1972).

Inhibitors: The enzyme is inhibited by surface-active reagents such as dodecyl sulfate, alcohols and fatty acids (Smith and Stoker 1949). Imidazole and indole derivatives are inhibitors via formation of change-transfer complexes (Shinitzky et al. 1966; Swan 1972).

Stability: Lysozyme stored as a dry lyophilized or crystalline powder at 2 - 8°C is stable for years. Solutions at pH 4-5 are stable for several weeks refrigerated and for days at ambient temperatures.

Mintz et al. (1975) have described a sensitive fluorimetric assay.