Question

What is the enzyme that cleaves the branch points in starch?

Answer 1

The use of enzymes in starch hydrolysis

Starch is the commonest storage carbohydrate in plants. It is used by the plants themselves, by microbes and by higher organisms so there is a great diversity of enzymes able to catalyse its hydrolysis. Starch from all plant sources occurs in the form of granules which differ markedly in size and physical characteristics from species to species. Chemical differences are less marked. The major difference is the ratio of amylose to amylopectin; e.g. corn starch from waxy maize contains only 2% amylose but that from amylomaize is about 80% amylose. Some starches, for instance from potato, contain covalently bound phosphate in small amounts (0.2% approximately), which has significant effects on the physical properties of the starch but does not interfere with its hydrolysis. Acid hydrolysis of starch has had widespread use in the past. It is now largely replaced by enzymic processes, as it required the use of corrosion resistant materials, gave rise to high colour and saltash content (after neutralisation), needed more energy for heating and was relatively difficult to control.

Answer 2

None of the enzymes discussed so far can hydrolyze the α-1,6 bonds present in starch. These branch points are cleaved hydrolytically by the debranching enzyme (EC 3.2.1.41), which releases linear oligosaccharides for further metabolism by amylases or phosphorylase.