Immunoglobulin synthesis and secretion, IV. Sites of incorporation of sugars as determined by subcellular fractionation.

P(3)K cells were uniformly labeled with [(14)C]leucine and also for 1 hr with [(3)H]leucine, [(3)]galactose, or [(3)H]glucosamine. Subcellular fractionation of labeled cells was performed and the amounts of radioactive immunoglobulin G in each fraction were determined. The results indicate that amino acids are incorporated in the rough endoplasmic reticulum, galactose primarily in the smooth endoplasmic reticulum, and glucosamine at both sites. A small portion of radioactivity was found in the microsomal supernatant regardless of the radioisotope employed.