Synthetic resins or natural rubbers -- part of the class 520 ser – Physical treatment of natural rubber or natural rubber... – Protein removal or conversion
Reexamination Certificate
2001-11-08
2004-08-31
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Physical treatment of natural rubber or natural rubber...
Protein removal or conversion
C528S934000, C528S935000
Reexamination Certificate
active
06784281
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of preparing a natural rubber latex and a method of preparing a deproteinized natural rubber latex, which are less likely to cause allergy, and a low allergenic natural rubber and a deproteinized natural rubber.
Natural rubbers have widely been used in various fields, for example, household appliances such as glove, medical appliances such as surgical glove and various catheters, lactation appliances, contraceptive device and the like because of features such as large extension, high elasticity and strong film strength. It has recently been reported that, when using medical appliances made of the natural rubber, such as surgical glove and various catheters, immediate (I type) allergy, which shows symptoms such as respiratory distress and anaphylactoid symptom (e.g. vascular edema, urttication, cyanosis, etc.), is caused. It is presumed that such immediate allergy is caused by a protein, as an antigen, in the natural rubber.
Accordingly, a trial of highly removing a protein in a natural rubber latex has recently been made and Japanese Patent No. 2,905,005 [Japanese Published Unexamined Patent (Kokai Tokkyo Koho Hei) No. 6-56902] discloses a method of adding a proteolytic enzyme such as alkali protease and a surfactant in a natural rubber latex, thereby subjecting to a deproteinization treatment, and sufficiently washing the latex by a centrifugation treatment.
According to the method described in the above patent publication, the protein in the natural rubber can be highly decomposed and removed. Specifically, the amount of the protein contained in the natural rubber, which is represented by the nitrogen content (N%) as determined by the Kjeldahl's method, can be controlled to a very low value such as 0.02% or less. It is generally presumed that the natural rubber is a mixture of a high-molecular component having a number-average molecular weight <Mn> of 1,000,000 to 2,500,000 and a low-molecular component having a number-average molecular weight of 100,000 to 200,000, the former high-molecular component being formed by mutually bonding the low-molecular components via peptide molecules contained in the natural rubber. Assuming that the molecular weight of the low-molecular component, which is deemed to be formed by original biosynthesis, is 100,000 and one peptide molecule in an intermolecular bond, i.e. one nitrogen atom (atomic weight: 14) is bonded based on one rubber molecule of this low-molecular component, the nitrogen content of the natural rubber is 0.014%. Accordingly, it is considered that about 0.02% of nitrogen is inevitably remained even if subjected to a high deproteinization treatment.
In case of subjecting to the deproteinization treatment by the method described in the above publication, an infrared absorption spectrum at 3280 cm
−1
peculiar to polypeptide is not observed in a rubber film formed by using the treated natural rubber latex. Therefore, it has been found that decomposition and removal of the protein are highly achieved by the method described in the above publication.
However, as is apparent from recent studies, there still exists a possibility of exhibiting allergy even if the protein is decomposed and removed through various conventionally known deproteinization treatments, including the method described in the above publication.
According to the present inventors,
(i) analysis was carried out by an analysis system of a protein, comprising a combination of a time of flight (TOF) type mass spectrometer and a two-dimensional surface decorative chip so as to confirm what degree a protein and a decomposition product thereof are remained in a natural rubber latex subjected to a deproteinization treatment by a conventional method, and
(ii) in vitro measurement based on an antigen-antibody reaction using serum of human patients was carried out in place of conventional in vivo measurement by a patch test so as to confirm allergy of a natural rubber latex subjected to a deproteinization treatment by a conventional method.
As a result, it has been found that:
(I) a protein or protein decomposition product having a number-average molecular weight <Mn> of about 4500 to 4700 is remained and the protein is not sufficiently decomposed, and
(II) an allergenic protein is included in the amount enough to cause immediate allergy even after the deproteinization treatment.
The term “allergenic protein” is defined as follows in the present Invention. Any protein and decomposition product thereof (hereinafter referred to as a “whole protein”) in a sample of a natural rubber latex contain the group of an “antigen protein” capable of producing an antibody in human serum. Antibodies produced in human serum are classified into an IgE-antibody capable of causing an allergic reaction and an antibody other than an IgE-antibody capable of causing no allergic reaction. Among the “antigen protein”, the antigen protein capable of producing the IgE-antibody, which can cause the allergic reaction, is referred to as an “allergenic protein” so as to distinguish from other antigen proteins.
Thus, an object of the present invention is to provide a method of preparing a low allergenic natural rubber latex which substantially contains no allergenic protein and is therefore less likely to cause allergy.
Another object of the present invention is to provide a method of preparing a deproteinized natural rubber latex which substantially contains no allergenic protein and is therefore less likely to cause allergy.
Still another object of the present invention is to provide a natural rubber latex which is less likely to cause allergy because of high degree of the decomposition of a protein.
Further object of the present invention is to provide a deproteinized rubber latex which is less likely to cause allergy because of high degree of the decomposition and removal of a protein.
SUMMARY OF THE INVENTION
(I) The method of preparing a low allergenic natural rubber latex of the present invention has a feature that it comprises adding a protease having an exopeptidase activity to a natural rubber latex and aging the natural rubber latex, thereby to decompose a protein in the latex to such a degree that the protein and a protein decomposition product, which have a number-average molecular weight of 4500 or more, are not detected.
(II) The method of preparing a deproteinized natural rubber latex of the present invention has a feature that it comprises adding an alkali protease to a natural rubber latex, thereby to decompose a protein in the latex, adding a protease having an exopeptidase activity, thereby to further decompose the protein and a decomposition product thereof in the latex, and removing the protein and the decomposition product thereof.
(III) The low allergenic natural rubber of the present invention has a feature that it is a natural rubber obtained by a decomposition treatment of a protein, wherein the protein and a protein decomposition product, which have a number-average molecular weight of 4500 or more, are not detected.
(IV) The deproteinized natural rubber of the present invention has a feature that it is a natural rubber obtained by a decomposition treatment and a removing treatment of a protein, wherein the content of the protein is 0.02% or less in terms of a nitrogen content, an absorption at 3280 cm
−1
is not recognized in an infrared absorption spectrum, and the protein and a protein decomposition product, which have a number-average molecular weight of 4500 or more, are not detected.
A protease (proteolytic enzyme) used in a conventional deproteinization treatment is a protease produced mainly by bacteria, and the protease has an optimum pH in an alkali range and also has an endopeptidase activity but does not exhibit an exopeptidase activity. The reason why the alkali protease was mainly used in a conventional deproteinization treatment is as follows: (a) a field latex as a natural rubber is supplied in the form of a so-called ammonia latex prepared by concentra
Hayashi Masaharu
Ichikawa Naoya
Miyamoto Yoshiaki
Birch & Stewart Kolasch & Birch, LLP
Nutter Nathan M.
Sumitomo Rubber Industries Ltd.
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