Origins and Structures of Multiple Forms of Enzymes

Abstract

The definition of isoenzymes as the products of distinct structural genes implies that those multiple enzyme forms which fall within its scope will differ to a greater or lesser extent in their amino acid sequences. In turn, these differences in primary structure will also entail greater or lesser differences in the higher levels of protein structure. The interpretation of the differences between isoenzymes in structural terms is well advanced in several cases. However, the origins of other categories of enzyme heterogeneity, and therefore the differences in structure existing within them, are in general much less clearly understood.