Use of contact prints for recording polyphenoloxidase isoenzymes separated by electrophoresis

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Abstract
Crude extracts of polyphenoloxidase (PPO) (E.C. 1.14.18.1) from a variety of food and plant sources were subjected to polyacrylamide gel electrophoresis. Following electrophoresis, the gels were stained for enzyme activity using catechol and L‐dopa as substrates. Contact prints were made of the enzyme stained gels 30 min after enzyme staining and on the following day. The negative images (white bands on a dark background) clearly showed the number, type, mobility and variation in enzyme staining of isoenzyme forms of PPO separated by electrophoresis. Contact prints were used to identify PPO isoenzyme forms in the leaves, stipules, roots, and stems of broad beans. This method was also used to demonstrate that a single isoenzyme form of PPO in broad bean leaves decreased with leaf age. Photographs, using professional rapid process X‐ray copy film, were also taken of enzyme stained gels for comparison to contact prints. Using contact prints, permanent records of PPO isoenzyme forms can be obtained rapidly, are inexpensive, and reproduce actual gel patterns.