Enzymatic activity was measured individually in octopuses at the end of the
20 day feeding period. Enzymatic activity of animals fed alginate-bound crab
meat was not determined due to the high mortality observed in octopus fed this
diet.
Salivary (posterior) and digestive glands were dissected and stored at
−40 °C until assayed. All animals were fasted 12 h before sampling. Frozen
samples were homogenized at 4 °C in 500 μL ice-cold pyrogen-free water.
Homogenates were centrifuged at 13,200 rpm(change to ×g) for 20 min at 4 °C.
The supernatant was diluted in 10 volumes of ice-cold pyrogen-free water.
Homogenates were immediately used for enzyme assays. The soluble-protein
content was measured in diluted homogenates (Bradford, 1976) using the BioRad
protein determination kit (Biorad@-500-0006). Samples were read in a
Biorad model 550 microplate reader at 495 nm. All assays were run in duplicate.
General proteases activity was measured in homogenates using azocoll
(Sigma A-4341) as substrate in phosphate buffer, pH 7. Absorbance was read
with a spectrophotometer (Spectronic model 21D) at 520 nm. One unit is defined
as the amount of enzyme that catalyzes the release of azo dye causing a
ΔA/Δt= 0.001 min−1
. Trypsin activity was measured in diluted (1:100) homogenates
using benzoil-arginine-para-nitro-anilide (100 mM BAPNAl) as substrate
in a buffer (0.1 M Tris, 0.05 M NaCl, pH 7.5) at 4 °C. Absorbance was
read at 405 nm. Leucine amino peptidase (Leu-amino peptidase) was measured
in diluted (1:10) homogenates using 100 mM L-leucine-p-nitro-anilide (LPNA)
as substrate in a buffer (0.1 M Tris, pH 8) at 25 °C. Absorbance was read at
410 nm.