Coalho Transgênico
Autor: Luiz Meira | Publicado: 2015-01-05T19:39:00-02:00




Disponibilizo os detalhes de dois tipos de&nbsp;coalho&nbsp;utilizado entre nós a título de exemplo como os transgênicos&nbsp;estão disseminados de forma subliminar em nosso cotidiano



CHY-MAX® MQuimosina oriunda do&nbsp;OGM&nbsp;Aspergillus niger utilizada para queijos






CHYMOSINS&nbsp;FROM GENETICALLY MODIFIED MICROORGANISMS

CHYMOSINS A AND B FROM GENETICALLY
    MODIFIED MICROORGANISMS

    First draft prepared by Dr F.S.D. Lin,
    Division of Toxicological Review and Evaluation
    Center for Food Safety and Applied Nutrition,
    US Food and Drug Administration

    1.  EXPLANATION

         Chymosins A and B derived from genetically modified
    microorganisms have not been previously evaluated by the Joint
    FAO/WHO Expert Committee on Food Additives.

         Chymosin, commonly known as rennin, is the principal milk-
    coagulating enzyme present in rennet.  Rennet, which has a long and
    extensive history of safe use in making cheese and other dairy
    products, is commercially prepared by aqueous extraction of dried
    fourth stomach of unweaned calves.  The aqueous extract contains a
    chymosin precursor, prochymosin, which is subsequently converted to
    enzymatically active chymosin.  Commercial preparations of calf
    rennet contain two forms of chymosin, A and B, usually in the
    proportion of about 40% of A and 60% of B.  Health aspects of rennet
    as a food ingredient were reviewed and evaluated at the fifteenth
    meeting of the Joint FAO/WHO Expert Committee on Food Additives in
    1972 (Annex 1, reference 26).

         Biochemically, chymosin (IUB No. 3.4.4.3) is a protein
    consisting of a single polypeptide chain of 323 amino acids with
    intramolecular disulfide linkages.  Chymosins A and B have been
    shown to differ only by one amino acid in the polypeptide chain; the
    former has an aspartic acid residue at position 286, whereas the
    latter has a glycine residue at the same position.

         Chymosin is produced intracellularly as preprochymosin. 
    Preprochymosin is shortened by 16 amino acids during secretion and
    appears in the stomach as prochymosin, which, in turn, is activated
    to chymosin by cleavage of an additional 42 amino acids.

         As a proteolytic enzyme, chymosin hydrolyses a specific bond in
    kappa-casein of milk, cleaving it into two peptides, para-kappa-
    casein and a macropeptide.  In milk, kappa-casein acts as a micelle
    stabilizer.  After this activity is destroyed by chymosin, milk
    coagulation occurs.  Chymosin A slightly exceeds chymosin B in
    proteolytic activity, whereas chymosin B is more stable at low pH
    (&lt; 3.5) than chymosin A.

         In recent years recombinant DNA technology has made it possible
    to obtain calf chymosin as a fermentation product from
    nontoxicogenic and nonpathogenic strains of bacterium, yeast or

    filamentous fungus, which have been transformed with a plasmid
    vector containing a DNA sequence coding for the chymosin precursor. 
    Available biochemical evidence has established that the transferred
    prochymosin sequence can be expressed correctly in the new host
    organisms.  The prochymosin product has the same molecular weight as
    prochymosin found in calf rennet and it can be cleaved into chymosin
    that has the same chemical, physical and functional (enzymatic)
    properties as its mammalian counterpart.

         The three recombinant chymosins that were reviewed in this
    monograph, as well as their respective production organisms are
    identified below:

         (1)  chymosin A from  Escherichia coli K-12

         (2)  chymosin B from  Kluyveromyces lactis, and

         (3)  chymosin B from  Aspergillus niger var.  awamori.

    1.1  Chymosin A produced from  Escherichia coli K-12 containing
         calf prochymosin A gene