Fate of ecto‐NAD+ glycohydrolase during phagocytosis of normal and mannosylated latex beads by murine macrophages

Abstract

In order to gain a better understanding of the role of ecto-NAD+ glycohydrolase, an enzyme predominantly associated with phagocytic cells, we have studied its fate in murine macrophages (splenic, resident peritoneal and Kupffer cells) during phagocytosis of opsonized on mannosylated latex beads. In parallel, we have also monitored nucleotide pyrophosphatase, another ecto-enzyme of macrophages. Phagosomes were isolated by flotation in a discontinuous sucrose gradient and the enzyme activities were determined with fluorometric methods. Low levels of NAD+ glycohydrolase and nucleotide pyrophosphatase could be measured associated with the phagosomal fractions, eg, respectively less than 4.5% and 10% in spleen macrophages. The phagosomal activities originate from the plasma membrane, ie they were latent and inactivation of ecto-NAD+ glycohydrolase with the diazonium salt of sulfanilic acid resulted in a marked decrease of this enzyme activity in the phagosomal fractions. Pre-labelling of the cell surface by [3H]-galactosylation indicated that NAD+ glycohydrolase is internalized to a lesser extent than an average surface-membrane unit. These results indicate that if ecto-NAD+ glycohydrolase of macrophages can be internalized to a limited extent during phagocytosis of opsonized or mannosylated latex beads, this enzyme appears to be predominantly excluded from the surface area involved in the uptake of such particles.