Читать книгу Introduction to the Human Cell - Danton PhD O'Day - Страница 18

The issue of membrane fluidity took on new meaning when human and mouse cells were induced to fuse and the behavior of their surface proteins was followed (Figure 2.13). The key to understanding this experiment is that antibodies were produced that detected specific proteins unique to either human or mouse cells. These proteins were thus antigens for the specific antibodies. By tagging the antibodies with different fluorescent dyes, it was possible to follow the localization of both the human protein antigen and the mouse antigen. In this experiment the human antibody was coupled with rhodamine, that fluoresces red when viewed under ultraviolet (UV) light with a microscope. The mouse antibody was conjugated to fluorescein isothiocyanate, more commonly called FITC, which fluoresces green under appropriate UV light. These two fluorescent dyes, as well as others, are commonly used in human cell biology research.

Figure 2.13. The fusion of human and mouse cells showed that proteins in the cell membrane were able to move around.

When the cells were first fused, the human and mouse antigens remained localized to opposite sides of the fused cell. If the cells were kept cold, this localization changed very little. However, warming the cells to 37^OC led to an intermixing of the fluorescent dyes revealed by a change from separated red and green fluorescence to an intermixed “blue” fluorescence. This verified that the cell membranes were fluid and proteins within them could move around from one area to another.

In summary, we now know:

•The lipid phase of the cell membrane, as well as other membranes, is fluid

•Fluidity depends upon types of lipids, temperature, etc.

•Membranes fuse during cytokinesis (cell division after mitosis), exocytosis, phagocytosis, etc.

•Proteins define many of the functional aspects of membranes

•Some membranes are designed for fusion: e.g., sperm-egg, myoblasts

•Specificity of fusion is defined by membrane proteins