Infrared spectroscopy of human tissue. V. Infrared spectroscopic studies of myeloid leukemia (ML-1) cells at different phases of the cell cycle.

Infrared spectra of myeloid leukemia (ML-1) cells are reported for cells derived from an asynchronous, exponentially growing culture, as well as for cells that were fractionated according to their stage within the cell division cycle. The observed results suggest that the cells' DNA is detectable by infrared spectroscopy mainly when the cell is in the S phase, during the replication of DNA. In the G1 and G2 phases, the DNA is so tightly packed in the nucleus that it appears opaque to infrared radiation. Consequently, the nucleic acid spectral contributions in the G1 and G2 phases would be mostly that of cytoplasmic RNA. These results suggest that infrared spectral changes observed earlier between normal and abnormal cells may have been due to different distributions of cells within the stages of the cell division cycle.