In vivo incorporation of
[U]-14C-amino acids: an alternative protein labelling procedure
for use in examining larval digestive physiology
S.K. Tonheim, M. Espe, A.J. Raae, M.J. Darias, I. Rønnestad-2004
Aquaculture, 235(1-4): 553-567
Abstract:
A radioactive soluble model protein for studies of
protein digestion, absorption and amino acid (AA) metabolism in larval fish
was successfully produced in Atlantic salmon by oral administration of
uniformly [U]-14C-labelled amino acids followed by blood sample
withdrawal (48 h post-administration) and purification. The salmon serum
protein (14C-SSP) was characterised in terms of the protein
composition and specific activity of its amino acids. Most radioactivity was
found in the three most abundant serum proteins, which had apparent
molecular weights of 65, 75 and 120 kDa, respectively, of which labelling
was found in all the amino acid residues of the SSP that were analysed. The
digestibility of the 14C-SSP was tested by in vivo tube feeding
using early stages of Atlantic halibut and was found to be more efficiently
digested and utilised than the 14C-methylated bovine serum
albumin (14C-BSA) that has been used in previous studies. This
supports the notion that proteins labelled by 14C-methylation are
not suitable as model proteins in metabolic studies due to modification of
their 14C-methylated lysine residues. Further studies on the 14C-SSP
demonstrated a digestibility of 59±13% in juvenile halibut, while at the
pre-metamorphic stage, it was only 25±13%. This supports the hypothesis
that there is a significant improvement in the ability to digest and utilise
dietary proteins as the digestive system becomes fully developed, including
a functional (acid-producing) stomach.