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A comparative study of xanthine oxidase in rat duodenum and liver was carried out by a histochemical technique, by cell fractionation and zone electrophoresis. With the histochemical method presented, reaction product could be demonstrated in the epithelial cells of the duodenal villi in glutaraldehyde-fixed cryostat sections incubated in 0.2 M sodium phosphate buffer at pH 7.4 containing 2.5 x 10 -3 M hypoxanthine and 1 mg/ml nitro-blue tetrazolium (Nitro-BT). No reaction product could be observed, however, in similarly treated sections of rat liver. Liver and duodenal homogenates showed high enzyme activity when assayed by a microfluorometric method using 2-amino-4-hydroxy pteridine as substrate. Fractionation of these homogenates revealed the presence of enzyme activity only in the high speed supernatant fraction. This fraction was also studied by zone electrophoresis on vertical starch gel and by acrylamide gel, disc electrophoresis. Xanthine oxidase separated electrophoretically into two distinct bands and was localized by incubation of the gels in the same medium as described for the histochemical method. The duodenal enzyme showed a more rapid mobility than that of the liver. The inability to demonstrate the hepatic enzyme histochemically is believed to depend on the lower concentration of the enzyme in liver as compared with its concentration in the duodenal mucosa.
Muriel Lazarus Sackler (Fri,) studied this question.