DEGRADATION OF PROTEINS MICROINJECTED INTO CULTURED MAMMALIAN-CELLS

Iodinated proteins were degraded after injection into HeLa cells at first‐order rates with half‐lives varying from three hours for the trout nonhistone chromosomal protein, HMG‐T, to 60 hours for whale myoglobin. Fluoresceinated‐bovine serum albumin (fl‐BSA) was degraded almost twice as fast as unmodified BSA. The rate of degradation of 125I‐BSA was very similar in eight cell lines of mouse, human, monkey and rat origin. Microinjected proteins were analyzed on SDS‐acrylamide gels after injection, and for BSA and immunoglobin G, all remaining intracellular 125I migrated at the molecular weight of the injected proteins. By contrast, more than 80% of the extracellular 125I chromatographed as iodotyrosine. With the exception of fl‐BSA, which exhibited perinuclear accumulation in approximately one‐half of the injected cells, autoradiography showed that throughout the period of study the injected proteins remained dispersed in the cytoplasm. Copyright © 1979 Wiley‐Liss, Inc.