AN INVESTIGATION INTO THE REMOVAL OF ENZYMES FROM PAPER FOLLOWING CONSERVATION TREATMENT
THERESA MEYER ANDREWS, WILLIAM W. ANDREWS, & CATHLEEN BAKER
1. Enzymes are complex proteins produced by living cells that catalyze specific biochemical reactions usually at body temperature (98.6°F or 37°C). Enzymes are usually sold in powder form and are obtained from animal, plant (particularly fungal), and bacteriological sources. In addition to their source designation, enzymes are also described in terms of unit definition, activity, and purity.
2. The α-amylases attack randomly along the amylose chain (the major component of wheat starch) to convert it into dextrins (short-chained polysaccharides), which are very water soluble. The β-amylases attack amylose only from one end at a time and are therefore much less effective compared to α-amylases. Diastases contain both α- and β-amylases and, therefore, are not as effective as the α-amylases alone. Proteases cleave the bonds of proteins leading to shorter chain polypeptides and finally to amino acid molecules, which are water soluble. Trypsins, which come from the ferments of pancreatic juices, reduce proteins to water soluble peptones.
3. The methods used to define units, or in other words to assay the enzyme, are based on standardized reactions of enzymes with compounds that are not dealt with in conservation. It should not be assumed that the conditions used in the assay (e.g., pH, temperature) and given in a catalog or on the enzyme bottle label are the optimum conditions for that enzyme. To determine the optimum pH for a specific enzyme, it is necessary to consult the enzyme literature.
4. It is important to note that the pH of an enzyme solution has a direct bearing on its effectiveness. Most enzymes have optimum efficiency at a specific pH. An enzyme solution, not buffered to maintain the optimum pH, might still be effective, but the required action would occur very slowly, perhaps appearing not to work at all. In order to control the pH carefully at the required optimum, buffers are often used. Common buffers to control the pH of enzyme solutions include sodium phosphate and sodium acetate, but conservators have been somewhat reluctant to use them because these buffers might leave deleterious residues.
5. The correct rpm setting for any particular centrifuge can be ascertained by spinning trial columns with a mixture of blue dextran and potassium ferricyanide. The optimal rpm is the minimum that allows the dextran (blue) to elute from the column while retaining the ferricyanide (yellow) on the column. In general, 1,000 rpm is sufficient.
6. The purity of an enzyme is based on two things: (1) the percentage of protein (i.e., enzyme(s)), in the solid, and (2) the homogeneity of the protein fraction (the presence of one or more enzymes). The designation “crude” therefore could indicate that there is not much protein in the solid and/or that the protein fraction is not homogeneous. Generally enzymes described as “crude” have not been recommended for use in paper conservation, but a crude enzyme does not necessarily mean that it cannot be used. Of particular importance to paper conservators is whether any other enzymes present in a crude preparation include undesirable ones, such as cellulase (or other cellulose-digesting enzymes). Unfortunately, at the present time it is not possible for a conservator to determine if a selected enzyme preparation contains any undesirable enzymes. It is not known whether the enzymes used in these experiments contain any cellulase, although it is doubtful that the pure A6380 does. Although A0273 was chosen for this experiment, we hesitate to recommend its use in paper conservation because of the possible existence of cellulase associated with this and other crude, fungal enzymes. For the time being, only mammalian or pure bacterial-source enzymes can be recommended with a significant degree of confidence.
SOURCES OF MATERIALSEnglish Paper, Cotton Fiber with Gelatin and Alum, Watermark:
J Whatman 1891Private collectionEnzyme, α-amylase: From Bacillus species, A6380, Type II-AEnzyme, α-amylase: fungal, crude, from Aspergillus oryzae, A0273, Type X-A
Sigma Chemical Co., St. Louis, Missouri 63178Japanese paper, Kizukishi, 100% Kozo,Japanese precipitated wheat starch, Zin shofu, 15% Paste after cooking, diluted for use
Conservations Materials Ltd., Sparks, Nevada 89431
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THERESA MEYER ANDREWS is currently an NEA advanced intern in paper and photographs conservation at the San Francisco Museum of Modern Art. She has an M.A. and Certificate of Advanced Study from the Art Conservation Department at the State University College at Buffalo. She has completed internships in both paper and photographs conservation at the California Palace of the Legion of Honor, the Metropolitan Museum of Art, the International Museum of Photography at George Eastman House, and with Jose Orraca. She has also worked with Debbie Hess Norris in her private practice and audited the photograph conservation block at the University of Delaware. Address: San Francisco Museum of Modern Art, Paper and Photographs Conservation, 401 Van Ness Avenue, San Francisco, Calif. 94102.
WILLIAM W. ANDREWS is currently a scientist at Chiron Corporation in Emeryville, Calif. He received his Ph. D. in biochemistry from the University of California, San Diego. He has worked at Synbiotics Corporation in San Diego and was also a postdoctoral research associate at the University of Buffalo, Main Street Campus. Address: Chiron Corporation, Horton Street, Emeryville, Calif. 94608.
CATHLEEN BAKER is associate professor of paper conservation in the art conservation department at the State University College at Buffalo. Before commencing her present teaching career in 1978, she was the paper restorer in charge of the Witt Collection of Drawings at the Courtauld Institute Galleries. She has an MA in art history from Syracuse University. She has given many conservation workshops, and was an instructor for the 1987 and 1991 ICCROM paper conservation courses. Address: Art Conservation Department RH 230, State University College at Buffalo, 1300 Elmwood Ave., Buffalo, N.Y. 14222.