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Enzymes which facilitate the industrial use and application of starch

16.01.2003

The cosmetic, textile, and food industries and even the construction industry use starch, the main energy reserve of plants, as a biodegradable and renewable substance for a variety of applications. To get to know the metabolism of this carbohydrate better and thus facilitate its industrial use and application, Milagros Rodríguez López proposed, in her PhD thesis, the identifying and isolating of the enzyme (or enzymes) responsible for the degradation activity of the precursor molecule for starch: ADP glucose.

This PhD work was directed by Francisco Javier Pozueta Romero at the Institute of Agrobiotechnology and Natural Resources (IARN), a centre of investigation jointly run by Consejo Superior de Investigaciones Científicas (Council for University Scientific Research), the Navarre Government and Navarre Public University.

Considerable quantity of starch in plants

Currently, practically all of industry uses starch and/or its derivatives in some way or another. Starch is used, amongst other things, for the manufacture of biodegradable photographic films, in adhesives, packing materials, detergents, paints and plastics; medical care products, shampoos, creams and lotions, cleansing products and cosmetics; or in the food and drinks industries for producing thickening agents which enhance the uniformity, stability and consistency of foodstuffs.

The widespread use of starch in industry explains the numerous research projects being carried out in order to better understand the biosynthesis process of the carbohydrate in plants and of its equivalent in bacteria: glycogen. However, although many studies have been carried out on starch is formed, what substances impede its synthesis have not been investigated in any depth.

Barley leaves

The conclusion of this doctoral thesis is that, both the accumulation of starch in plants and of glycogen in bacteria is highly determined by the enzymatic activities that synthesise ADP glucose and by those that degrade it. Moreover, in the opinion of Milagros Rodríguez López, ADP glucose is not just a precursor molecule for glycogen and starch, but plays a versatile role at the point of diversification of several metabolic routes.

The authoress’ research has identified two proteins as being possibly responsible for the breaking down of ADP glucose and which, thus, on the breaking up of the ADP glucose molecule, impede the formation of starch in plants. Professor Milagros Rodríguez chose to do the tests on barley leaves as it is in this tissue that enzymatic activity is highest.
The objective then was to isolate the enzyme or enzymes responsible for this enzymatic activity.

In order to carry this out, various techniques were used such as ultracentrifuging or precipitation with ammonium sulphate in order to isolate enzyme or enzymes responsible. According to the results, there are a number of isoforms responsible for the hydrolysis of ADP glucose in the higher plants, which impede the biosynthesis of starch.

As a result of this research, two enzymes have been identified as being possibly responsible for the enzymatic activity: NPP1 (Nucleotide Phosphatase Phosphodiesterase 1) and NPP2 (Nucleotide Phosphatase Phosphodiesterase 2). Subsequently, molecular biology work was carried. Thus the gene sequences were identified and a way of confirming whether these proteins were really responsible for the enzymatic activity or not.