GLYCOTRIPEPTIDES ARE RELEASED BY YEAST BUT NOT BY MAMMALIAN MICROSOMES

Glycotripeptides generated in vivo in the endoplasmic reticulum (ER) h ave been used as markers to assess the rate of vesicular bulk flow fro m the ER via the Golgi apparatus to the plasma membrane in mammalian c ells. The applicability of such glycotripeptides as markers for bulk f low along this pathway has been questioned by a report on non-vesicula r release of glycotripeptides from yeast semi-intact spheroplasts. We have therefore investigated direct release of glycotripeptides from ye ast and from mammalian microsomes and report here that such release is specific to the yeast system and cannot be detected in mammalian micr osomes.