The History of Invertase: 165 Years of Biochemistry

The story of invertase begins in the 1850s and 1860s with the study of fermentation and the optical properties of sugar solutions. Louis Pasteur observed that yeast converted sucrose into fermentable sugars and that the fermentation solution showed an inversion of optical rotation. Marcellin Berthelot in 1860 demonstrated that cell-free yeast extracts could perform this inversion, publishing the first description of the enzyme he called 'invertine' — establishing that it was a substance produced by yeast, distinct from the cell itself. This predated the word 'enzyme' by more than two decades.

Emil Fischer's 1894 lock-and-key hypothesis of enzyme specificity was developed partly from observations of invertase and related glycoside-cleaving enzymes. Fischer noted that invertase cleaved alpha-glucosides and beta-fructosides but not the corresponding epimers — a stereochemical specificity that implied a geometrically complementary relationship between enzyme and substrate. He articulated this as the lock (enzyme active site) and key (substrate) analogy. Fischer received the Nobel Prize in Chemistry in 1902 for his work on sugar and purine chemistry, which included foundational work on enzyme specificity.

James Sumner crystallized urease in 1926, the first enzyme to be isolated in crystalline form, proving that enzymes were proteins — a claim that was initially controversial. Following Sumner's demonstration, other enzymes were crystallized in the 1930s, including invertase preparations. The crystallization era established that enzymes had defined molecular structures, paving the way for protein chemistry and eventually structural biology. Sumner received the Nobel Prize in Chemistry in 1946 for his crystallization work.

With the rise of molecular biology, invertase became a model for studying gene regulation, protein secretion, and glycosylation in Saccharomyces cerevisiae. The gene encoding yeast invertase, SUC2, was cloned in the early 1980s. The discovery that invertase exists in two forms — a secreted, highly glycosylated form and a smaller, intracellular, non-glycosylated form from the same gene — became a model for studying signal peptide function and post-translational protein trafficking. Mutations in the SUC2 signal peptide were used to map the requirements for secretion in yeast, work that informed understanding of the secretory pathway in all eukaryotes.