Page 6 - ALLEN'S COMMERCIAL ORGANIC ANALYSIS A TREATISE ON THE PROPERTIES, MODES OF ASSAYING... VOL VIII

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ENZYMES
Proteoclasts...... Pepsin, trypsin, erepsin, rennin 0 •
Lipoclasts.. .....Lipase
Oxydases .... ..Laccase,' tyrosinase, peroxydase, catalase
Enzymes being measured by their activities, it is fundamental that
the amount of enzyme shall be proportional to the change produced.
The numerous investigations on the kinetics of enzyme action have
established that this relation only holds when the amount of enzyme
is relatively small compared to the amount of the substance on which
it acts and, further, the change must not exceed the conversion of
about 3o or 40% of the original substance. The latter part of this
statement, which virtually includes the first part also, is commonly
referred to as Kjeldahl's law of proportionality. Kjeldahl stated
originally, that the amount of reducing sugar formed by the action
of malt extract upon an excess of starch was a true measure of the
diastatic power, so long as the digestion was not carried beyond the
point corresponding to 4o conversion of the starch. He showed
that up to this point the velocity curve could be expressed by a
straight line.
Enzymic activity may be expressed as () the amount of change
produced by a given amount of enzyme in a given time, (2) the amount
of enzyme required to produce a given change in a given time, or (3)
the time required for a given amount of enzyme to effect a given change.
In addition to these three factors the temperature of the change and
all other conditions must be maintained constant, particularly those
likely to introduce alkaline impurities, e.g., the use of ordinary glass
apparatus. Lastly, the hydrolyte must either be chemically pure or
such bulk of it be acquired as will suffice for a large number of com-
parative experiments.
Neglect of these precautions in the case of diastase or invertase
may lead to altogether false values.
In investigating extracts of leaves or plant material for enzymes the
influence of tannin in rendering the enzymes inactive must not be over-
looked. Brown and Morris (Trans., 1893, 63, 60) have shown that
the comparatively weak diastatic action of some leaves is due to
the tannin they contain. The writer has found this to apply to emul-
sin and other enzymes including the oxydases. The tannin also inter-
feres with the estimation of sugars by Fehling's method. It is precipi-
tated from the leaf extract by means of basic lead acetate; the solution
is filtered, the volume of the filtrate noted and the lead precipitated by
Since the specific nature of_the oxydases is most uncertain, it is preferable to use the
general term oxydase instead of laccase
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