Blackman found that increased temperature increases
the rate of the dark carbon-reducing reactions, but only up
to about 35°C. Higher temperatures caused the rate to fall
off rapidly. Because 35°C is the temperature at which many
plant enzymes begin to be denatured (the hydrogen bonds
that hold an enzyme in its particular catalytic shape begin
to be disrupted), Blackman concluded that enzymes must
carry out the dark reactions.