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ENZYMES. 55
tive influences (heat, alkalies) 1
;
According to this only that part of the
added enzyme which is combined with the substrate is active. In
judging of the rapidity of enzyme reactions the following must he con-
sidered:
1. The velocity with which the enzyme combines with the substrate.
2. The result of the division, i.e., how much of the added enzyme
is combined with the substrate.
3. The velocity of the chemical processes produced by the enzyme.
The velocity of the combination of the enzyme with the substrate (1) can at
least in many cases be ignored in consideration of the time necessary for the
chemical reaction (see page 37). This applies to those cases where the chemical
transformation in the presence of an excess of substrate at the beginning of the
processes remains the same in each successive time interval. The quantity of
enzyme combined with the substrate, does not, in these cases, increase with the
time, which would be the case if the time necessary for the combination is not in
comparison with that for the chemical reaction. Equal decomposition for equal
time at the beginning of the processes have been found for the following enzymes
—
invertase, 2
diastase, 3
trypsin with casein, 4
as substrate.
The second question, as to the division of the enzyme between different phases
we will discuss after we have spoken of the velocity of the real chemical reaction
(page 58) as well as the retardation of enzyme action (page 62).
In regard to the chemical reaction they proceed probably in a different
manner according to the kind of combination between the substrate and
the enzyme. In one case we can consider that the combination of the
enzyme with the substrate is of such a kind that both form a homogeneous
phase and that one serves as solvent for the other (page 27). In this
case the chemical reaction produced by the enzyme takes place in a
homogeneous medium. Secondly, we can consider the combination of
the substrate and enzyme as an adsorption combination (see page 27)
in which case the combination does not form a homogeneous phase and
the reaction differs more or less from one taking place in a homogeneous
system. Bearing this in mind it would be interesting to investigate
whether the facts found for enzymotic reactions correspond with
catalytic reactions in homogeneous media.
For these latter the following laws (see page 33) have been found:
1. When the quantity of catalyst remains constant, the reaction
1
O’Sullivan and Thompson, Journ. Chem. Soc, 57, 926 (1890); Bayliss and Starling,
Journ. of Physiol., 30, 71 (1903); Hedin, ibid., 30, 173 (1903); 32, 474 (1905); Taylor,
Journ. of biol. Chem., 2, 90 (1906).
2
O’Sullivan and Thompson, Journ. Chem. Soc, 57, 926 (1S90); Ducleau, Traite.
de microbiologie II, 137; Brown, Trans. Chem. Soc, 81, 373 (1902); Armstrong,
Proc. Roy. Soc, 73, 500 (1904); Hudson, Journ. Amer. Chem. Soc, 30, 1160, 1564
(1908).
3
Brown and Gliddinning, Proc Chem. Soc, 18, 43 (1902).
• Hedin. Journ. of Physiol., 32, 471 (1905).
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