The fate of 14C-LDH5 after intravenous
and intraperitoneal injection was
studied in dogs and rats. The enzyme was
labelled by means of incorporating 14C-acetate
groups into the enzyme protein. The turnover
of extracellular 14C-LDH5 was investigated by
measurement of 14C-radioactivity, enzyme activity,
and by autoradiography.
The elimination of 14C-LDH5 takes place in the intravascular space, as well as in the
extravascular fluid compartments. Part of the 14C-LDH(5)-radioactivity is excreted in urine,
bile, and the gastrointestinal tract; a smaller amount remains in the organism. A specific
elimination organ cannot be distinguished, as the enzyme elimination is multilocal.
The significance of enzyme elimination in the diagnostic assessment of enzyme levels
in serum is indicated. The labeling of enzymes with isotopes and the behavior of cell
enzymes in the extracellular compartment are discussed, and the results are compared with
other results in the literature.