抄録
Decarboxylation of iodohistidines and histidine was comparatively examined by measurement of 14CO2 formation from 14C-iodohistidine (14C-MIH, 14C-DIH) and 14C-histidine during incubation with bacterial histidine decarboxylase or with rat liver homogenate. The decarboxylation rate of iodohistidines was higher than that of histidine, and the decarboxylation of DIH was much faster than that of MIH or histidine, without showing any time-lag. It may be suggested that iodohistidines are directly decarboxylated without deiodination by decarboxylase (s) and converted into the corresponding iodohistamines, which were identified with separately synthesized iodohistamines, by thin-layer chromatogram on cellulose, and it was found that the ratio of decarboxylated metabolites (iodohistamines) was higher than that of deiodinated products (MIH and histidine), and that deaminated metabolite (urocanic acid) was not detected in the metabolites. It was shown that decarboxylation is the major pathway of iodohistidine metabolism. Iodohistidines seemed to be decarboxylated non-specifically by enzymes (histidine decarboxylase, aromatic L-amino acid decarboxylase) in liver homogenate, since the decarboxylation rate of iodohistidines is higher in alkaline pH (indicating aromatic L-amino acid decarboxylase), but it is inhibited slightly by α-methyl-DOPA, an inhibitor of the enzyme.
