Scanning tunneling microscopy and atomic force microscopy visualization of the components of the skeletal muscle glycogenolytic complex

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Abstract
The muscle glycogenolytic complex is responsible for providing access to the reserve carbohydrate energy stores in skeletal muscle during times of vigorous exercise. The complex is a set of enzymes and regulatory factors that are bound to the carbohydrate storage polymer, glycogen. These components provide the ordered synthesis and utilization of that stored form of glucose. Glycogen and the enzyme proteins, phosphorylase and phosphorylase kinase, have been imaged by atomic force microscopy (AFM) or scanning tunneling microscopy (STM). The images of all three generally correlated well with the known features of those molecules, as measured by traditional physicochemical methods. The exception for all three polymers is that the measured height by STM is in error. In each case, the molecules appear to be only about 30% of their true thickness, as measured by height above the graphite surface. It is clear that both AFM and STM will play important roles in biomedical investigation of macromolecular structures and complexes.