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.