Comparison of14C-amino acid mixture and [35S]methionine labeling of cellular proteins from mouse fibroblast C3H10T1/2 cells by two-dimensional gel electrophoresis

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Abstract
Total Cellular proteins from mouse C3H10T1/2 fibroblasts were compared by two‐dimensional (2‐D) gel Electrophoresis after radiolabeling with [35S]methionine (35S‐Met) or 14C‐amino acids (14C‐AA). 35S‐Met labeling of protein was three to four times greater than 14C‐AA incorporation over a 24 h period. Automated comparative analysis of replicate fluorographs after 6, 12, and 24 h of labeling showed considerable homology between radiolabeling methods. More than 88% percent of 35S‐Met and 14C‐AA‐labeled proteins were common at each time point. However, the total number of 35S‐Met‐labeled proteins dropped from 6 to 24 h while the number of 14C‐AA‐labeled proteins increased. Additionally, twenty‐one proteins were uniquely labeled by 14C‐AA that were not detectable by 35S‐Met over the labeling period. Densimetric analysis showed that several 35S‐Met and 14CAA‐labeled proteins exhibited time‐related diferences in radiolabel incorporation while most proteins remained relatively constant. Protein patterns of silver‐stained gels from 6 to 24 h were highly registered and showed few qualitative differences. Proteins detected in radiolabeled gels were generally, but not always, found in silver‐stained gels. Thus, 35S‐Met appears better suited for short‐term radiolabeling of Cellular protein while more comprehensive labeling of protein occurs with 14C‐AA during prolonged incubation of Cell cultures under present experimental conditions.