Intracellular localization of mannan synthetase activity in budding baker's yeast

In extracts from budding yeast cells mannan synthetase is present at a much higher activity than in extracts from stationary cells. This activity is largely sedimentable. It is associated with fragments of the plasmalemma, with vesicles known to be involved in the local secretion of glucanases at the site of budding, and with ‘light membranes’ representing a mixed fraction which probably contains fragments of the endoplasmic reticulum. The possible involvement of these structures in the synthesis and secretion of mannanprotein is discussed.