Variations in Sulfhydryl, Disulfide, and Protein Content during Synchronous and Asynchronous Growth of HeLa Cells |
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| Authors: | F Mauro A Grasso and L J Tolmach |
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| Abstract: | The cellular contents of protein-bound and nonprotein sulfhydry (—SH) and disulfide (—SS—) groups were measured in both asynchronous and synchronous HeLa S3 cultures. About 90% of these groups are associated with proteins, the majority in the —SH form. The content of protein-bound groups, and hence the total content of —SH and —SS— groups (28 × 10-15 moles/cell, or 1.1 × 10-6 moles/g protein on average), changes in parallel with the protein content (which varies between 2 and 4 × 10-10 g/cell) as asynchronous populations pass from the lag through the exponential to the stationary phase of growth. The concentration of nonprotein —SH groups, in contrast, increases 10-fold during lag phase and decreases in stationary phase; it follows the protein concentration closely during the exponential phase, at a level of about 2.8 × 10-15 moles/cell. In synchronous cultures the protein content doubles during the cell cycle, possibly in an exponential fashion. The total —SH and —SS— content also doubles, but the rate of increase appears to fluctuate. The concentrations of the protein-bound groups show 2- to 3-fold fluctuations per unit protein: protein-bound —SH groups and mixed —SS— linkages rise to maxima while protein-bound —SS— groups fall to a minimum at the G1/S transition, and fluctuations in these groups occur again during G2. In addition, the protein-bound —SH concentration falls continuously during the S phase. The nonprotein —SH concentration undergoes the largest (relative) fluctuations, dropping from 4 × 10-15moles/cell in early G1 to about 0.4 × 10-15 moles/cell (of standard protein content) at the end of G1, and then rising to 30 times this value by the end of S. |
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