Stability, substrate and inhibitor specificity and electrophoretic
properties of a crude polyphenol oxidase (PPO) preparation extracted
from d'Anjou pears (Pyrus communis L.) were investigated. Levels
of polyvinylpyrrolidone and pH of buffer for extraction were found
to affect the specific activity of the extracted enzyme. An extract
prepared with 1.5 g insoluble PVP per 15 g fresh tissue in acetate
buffer (pH 5.6) resulted in the highest PPO specific activity of the
crude extract. Addition of PVP did not affect the electrophoretic
patterns of PPO isozymes. The pH optimum of PPO occurs at 7.0.
Heat inactivation of PPO followed first order kinetics and approximately
50% of PPO activity was inactivated after heating for 11.7,
6.25, 2.25 and 1.1 min at temperature of 70°,75°,80° and 85°C,
respectively.
The crude PPO enzyme was active towards o-dihydroxyphenols,
but inactive towards monophenols. Disc electrophoresis on 7% polyacrylamide gels revealed eight active isozymes towards catechol,
4-methylcatechol, chlorogenic acid, caffeic acid, dopamine,
d-catechin and DL-dopa. Similar electrophoretic patterns were
observed with all substrates. No differences in the band patterns
were observed between a fresh crude PPO preparation, a frozen
crude extract and a dialyzed extract when catechol was used as
substrate. L-cysteine, diethyldithiocarbamate, thiourea, metabisulfite,
cyanide, mercaptoethanol and ascorbic acid inhibited the
enzyme activity. L-cysteine and diethyldithiocarbamate were the
most effective inhibitors. / Graduation date: 1977
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27255 |
| Date | 17 September 1976 |
| Creators | Halim, David Husien |
| Contributors | Montgomery, Morris W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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