Amylo-1,6-glucosidase (debranching enzyme) in erythrocytes. (Preliminary communication)

Steinitz, K.

Harefuah 62: 275-278

1962


ISSN/ISBN: 0017-7768
PMID: 13916767
Document Number: 8236
The incorporation of C14-glucose into glycogen in the presence of tissue homogenate or lysed cells has been found to be dependent on the presence of amylo 1 : 6-glucosidase (debrancher enzyme). In the present communication the method of Hers for the determination of this enzyme has been adapted to measure its activity in red cells, and values for normal persons and cases of glycogen storage disease arc reported. 0.2 ml. of washed and lysed red cells were incubated for 6o or 120 minutes at 370 with o.o5 ml. uniformly labelled CH-glucose (1.5 microcuries), 0.2 mt. zo% glycogen, 0.05 ml. o.x M phosphate buffer pH 7.4, and 0.05 ml. 0.5M NaF. After removal of the hemoglobin with trichloracetic acid, the glycogen was alternately precipitated by alcohol and dissolved in water 5 times to insure complete removal of non-bound radioactive material. The radioactivity of a weighed amount of glycogen was counted and the incorporation of glucose into glycogen expressed as the per cent of the radioactivity incorporated per gm, hemoglobin per hour, The amylo-1 : 6-glucosidase of the red cells was determined in 5 normal subjects (7 determinations) and in 2 cases of glycogen storage disease with suspected deficiency of this enzyme (3 determinations). Fresh hemolyzate of normal persons shows an activity of 0.25- 1.87%. In suspected cases of debrancher deficiency the values are rather high, 0.87-1.15% in spite of prolonged storage of the hemolyzate in the deep freezer. Synthesis of glycogen is supposed to take place chiefly in nucleated red cells, while the mature erythrocyte is supposed to posses a greatly diminished UPDG-glycogen synthetase. Phosphorylase activity in mature erythrocytes has been found. Amylo-1 : 6-glucosidase activity in red cells is reported here for the first time. The demonstration of the debrancher enzyme in erythrocytes makes it certain that the breakdown of glycogen in these cells proceeds by the same twofold action of enzymes as in muscle and liver. The increased glycogen content of red cells in patients with debrancher deficiency has been ascribed to reduced activity of the latter enzyme in red cells. The demonstration of normal values of amylo-1 : 6-glucosidase in the red cells of 2 cases of increased glycogenosis due to deficiency of this enzyme makes this explanation of the cause of the increased glycogen content of the erythrocytes rather improbable. No other hypothesis can explain the increase of an abnormal glycogen in red cells in these cases, however, and we are for the time being unable to interpret these findings.

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Amylo-1,6-glucosidase (debranching enzyme) in erythrocytes. (Preliminary communication)