Interactions of a model block copolymer drug delivery system with two serum proteins and myoglobin.

mycelium from 24 h, reaching a maximum at 3-4 days then dcclining by day seven. Electron micrographs of the mycelium at later times was complicated by the state of the mycelium, but few granules could be seen. The granules, which were 100-400 A in diameter, appeared to be polysaccharide on the basis of periodic acid-thiocarbohydrazide-silver proteinate staining [ 21. Large amounts of lipid material were also present. Glycogen was extracted from mycelial samples of A. niger taken at daily intervals and estimated colorimctrically. The glycogen content of the mycelium increased up to the sixth day, then declined. The amount of glycogen measured suggests that the polysaccharide granules were glycogen. Glycogen synthetase activity was determined by measuring the amount of uridine diphosphate (UDP) formed from UDP glucose in the presence of glycogen and glucose 6-phosphate. UDP was estimated by the colorimetric determination of the pyruvate produced from phosphoenolpyruvate in the pyruvate kinase reaction. Glycogen synthetase activity was detected in all samples, reaching an apparent peak of activity on day seven, then declining until it returned the initial level on day ten (Table 1). The glycogen phosphorylase level was measured by the release of inorganic phosphate from glucose 1-phosphate when glycogen was synthesized. Phosphate was determined colorimetrically. Phosphorylase activity appeared to increase with time, although not linearly, with the greatest increase in activity on days nine and ten. The observed levels of the two enzymes were broadly consistent with the levels of glycogen observed at different times. Assuming that the synthetase is the major synthetic enzyme and that breakdown is due to phosphorylase, then the pattern of increasing synthetase activity over the first 7 days followed by a fall, with the level of phosphorylase rising in the latter stages would explain the observed glycogen levels. The late increase in phosphorylase activity coincides with the Table 1 . Glycogen conrenr and relored cnzymc cic~rit~iry