Abstract. a-mannosidases I and II (Man I and 11) are resident enzymes of the Golgi complex involved in oligosaccharide processing during N-linked glycoprotein biosynthesis that are widely considered to be markers of the cis-and medial-Golgi compartments, respectively. We have investigated the distribution of these enzymes in several cell types by immunofluorescence and immunoelectron microscopy. Man 1I was most commonly found in medial-and/or trans-cisternae but showed cell type-dependent variations in intra-Golgi distribution. It was variously localized to either medial (NRK and CHO ceils), both medial and trans (pancreatic acinar cells, enterocytes), or trans-(goblet ceils) cisternae, or distributed across the entire Golgi stack (hepatocytes and some enterocytes). The distribution of Man I largely coincided with that of Man II in that it was detected primarily in medialand trans-cisternae. It also showed cell type dependent variations in its intra-Golgi distribution. Man I and Man II were also detected within secretory granules and at the cell surface of some cell types (enterocytes, pancreatic acinar cells, goblet cells). In the case of Man II, cell surface staining was shown not to be due to antibody cross-reactivity with oligosaccharide epitopes. These results indicate that the distribution of Man I and Man II within the Golgi stack of a given cell type overlaps considerably, and their distribution from one cell type to another is more variable and less compartmentalized than previously assumed.

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Nucleotide pyrophosphatase and phosphodiesterase I of rat liver have been found to be localized primarily in cell particulates highly enriched with respect to the most commonly accepted plasma membrane marker, 5'-nucleotidase, and therefore should themselves be assigned a plasma membrane localization . The observation that plasma membranes sediment in isotonic sucrose with both nuclear and microsomal fractions was exploited to obtain plasma membrane preparations from each fraction . Both preparations are similar in chemical and enzymic composition . Moreover, the preparative method developed in this study appears to give the best combination of yield, purity, and reproducibility available . The question of the possible identity cf nucleotide pyrophosphatase and phosphodiesterase I is considered, and evidence is presented suggesting that these activities may be manifestations of the same enzyme.

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