The conformation of d-glyceraldehyde-3-phosphate dehydrogenase was studied by means of spectropolarimetry under various conditions. It was shown that at neutral pH the enzyme possesed a compact globular structure with approx. 40% α-helical content. When the pH was altered, a change in secondary and tertiary structure was observed which was manifested in the change of α-helicity and in the uncoiling of the molecules. Sodium dodecylsulphate produced a change in the tertiary and quaternary structure, i.e. uncoiling of the molecules and the division of the enzyme molecule into subunits, while the secondary structure remained unchanged. The coenzyme (NAD+) and the substrate (glyceraldehyde) produced conformational changes in the apoenzyme molecule. The results can be interpreted in terms of Koshland's "induced-fit" hypothesis.
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