The value of tunicamycin for studies on immunoglobulin biosynthesis.

1979). The intracellular activities of these enzymes were also inhibited (by approx. 50%) during culture in the presence of tunicamy cin. Mycelia of A. niger were incubated for 24 h in the presence of ~-[2-%]mannose. The radiolabelled proteins secreted into the culture medium were separated by polyacrylamide-gel electrophoresis. The results indicated that, in the presence of tunicamycin, the glycosylation of proteins that have the same electrophoretic mobility as the three glycosidases is inhibited (Speake et al., 1979). Antiserum specific for /?-N-acetylglucosaminidase was obtained after injection of the purified enzyme into rabbits. Immunotitration of the enzyme activity in the culture medium indicated that the decreased enzyme activity observed in the presence of tunicamycin was due to a decrease in the amount of immunodetectable enzyme (B. K. Speake, D. J. Malley & F. W. Hemming, unpublished work). There are a number of possible explanations for the decreased amount of enzyme in the culture medium during growth of A. niger in the presence of tunicamycin. Inhibition of glycosylation of the newly synthesized enzyme may lead to impairment of its secretion. No intracellular accumulation of /%N-acetylglucos aminidase was, however, observed. Secondly, it is possible that the non-glycosylated enzyme may be especially susceptible to proteolytic degradation, either before or after secretion from the cell. Finally, inhibition of the synthesis of the protein portion of the specific enzyme has not been ruled out, although tunicamycin was found to have little effect on total protein synthesis. Obviously more work is needed to distinguish between these alternative explanations. It is however evident that glycosylation is of considerable functional importance in the production of secreted enzyme by this organism.