125I-labeled human α-d-mannosidase (form A) was administered intravenously to rats and the tissue distribution and uptake of the radioactivity was measured in several different organs at various times following administration of the radioactive enzyme. The radioactivity per gram of tissue weight was calculated for several tissues and for serum. At each time period, the uptake by the organ was expressed as a percentage of the corresponding serum value. The results obtained for liver were: 34.22% after 10 min; 29.09% after 24 hr. Labeled human α-d-mannosidase (form A) was found in the kidneys: 13.30% after 10 min; 16.56% after 24 hr. Similar results were observed for the spleen: 10.59% after 10 min and 11.18% after 24 hr. After 1 hr, approximately half of the radioactivity in the liver was associated with liver particulate matter. The radioactivity could be dissociated from this material after freezing and thawing. Approximately 90% of the radioactivity recovered cochromatographed as the free enzyme. This fraction was partially purified by gel filtration on Sephadex G-200 and then subjected to polyacrylamide-gel electrophoresis. Its relative electrophoretic mobility was found to be identical to that of 125I-labeled and native α-d-mannosidase (form A).
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