The metabolism of proline and arginine was investigated in
kidney, gill, and heart of the pelagic squid, Symplectoteuthis. The rates of CO2
release from 14C-proline exceeded the rates from 14C-arginine. The metabolic
rate of arginine and proline was assessed by monitoring the incorporation of
arginine-derived carbon into various intermediates. Arginine was metabolized,
through ornithine, to proline as well as to glutamate and various subsequent
derivatives (alanine, octopine, aspartate, and carboxylic acids). The same components
became labeled using 14C-proline as the starting substrate, but only the
gill was capable of converting proline to arginine via the urea cycle. In addition,
14C-proline oxidation rates were high enough to exceed those of 14C-glucose in
at least three tissues, kidney, heart, and inner mantle muscle