Potato enzyme inhibitors

Heibges, A., Salamini, F., Gebhardt, C. (2003). Funetional eomparison of homologous members of three groups of Kunitz-type enzyme inhibitors from potato tubers Solanum tuberosum L.). Mol Gen. Genomics, 269,535-541. 

Enzyme inhibitors of a protein nature are of significant concern because of widespread occurrence. The most common of these affect the pancreatic enzymes, trypsin and chymotrypsin. and arc found in legumes, as well as in egg whites and potatoes. 

Taking an advantage of the existence of kinetic measurements data for several inhibitors of PAL from potato,111,112 ab initio investigation of the physical nature of enzyme-inhibitor interactions and the existence of correlation between particular energy components and inhibitors activity was conducted.58 Similarly to the above presented LAP study,54-58 the validity of successive approximations was tested to qualify a permissible level of simplification and - first of all - to reveal which constituents of interaction energy contribute the most to the specific inhibitors... 

Table II gives the results of residual trypsin inhibitor levels for the various soymilk preparations. The 90 and 120 sec microwave treatments were the most effective in inactivating the trypsin inhibitor complex while hot water treated and unheated samples showed the highest levels. It is not surprising to find that microwave processing is more efficient than hot water in suppressing trypsin inhibitor considering the rapid penetration of food material by microwaves and the susceptibility of protein action to small heat induced changes in tertiary structure. Hence, Collins and McCarty (12) found microwaves produced a more rapid destruction of endogenous potato enzymes (polyphenol oxidase and peroxidase) than hot water heating.

Figure 143 In vivo activities of four different digestive enzymes in adult bees after 8 days of feeding ad libitum on syrup with (a) 1, 3, or 10 mg/ml aprotinin or (b) 0.1 or 2 mg/ml potato protease inhibitor 1 (POT-1) added. Control bees were fed plain syrup without additive.

Enzyme inhibitors are also present, e. g., potatoes contain proteins which have an inhibitory effect on serine proteinases, while proteins from beans and cucumbers inhibit pectolytic enzymes. Protein and enzyme patterns, as obtained by electrophoretic separation, are often characteristic of species or cultivars and can be used for analytical differentiation. Figure 17.1 shows typical protein and proteinase inhibitor patterns for several potato cultivars. 

Many cereals and cereal products (such as wheat, rye, breakfast cereals and bread) contain proteins inhibiting animal, but not plant amylases. Invertase inhibitors are found in potato tubers, for example. The significance of these enzyme inhibitors is neghgible and the consequences of their presence in food are not yet known. It is beheved that amylase inhibitors could potentially be used in preparations for diets to promote weight loss. 

There is evidence that protease inhibitors selectively regulate the activity of specific digestive enzymes at the level of gene expression (Rosewicz et al., 1989). Specifically, soybean trypsin inhibitor increases secretion of proteases, including a form of trypsin that is resistant to inhibition but does not cause an increase in amylase secretion. Although the relationships between protease inhibitors and exocrine pancreatic secretion have received the most attention, pancreatic secretion is increased when potato fiber is added to the diet (Jacob et al., 2000), although the mechanism and signaling pathway have not been elucidated. 

Pyraflufen-ethyl is also used as the defoliant for cotton and as a desiccant for potatoes. Pyraflufen-ethyl is a novel inhibitor of protoporphyrinogen IX oxidase. Inhibition of this enzyme in chloroplasts causes accumulation of protoporphyrinogen IX, which results in peroxidation of foliar cell membrane lipids under the light and finally death of cells. 

AGIRE computer program for, 249, 79-81, 225-226 comparison to analysis based on rates, 249, 61-63 complex reactions, 249, 75-78 experimental design, 249, 84-85 inhibitor effects, 249, 71-75 potato acid phosphatase product inhibition, 249, 73-74 preliminary fitting, 249, 82-84 prephenate dehydratase product inhibition, 249, 72-73 product inhibition effects, 249, 72-73 prostate acid phosphatase phenyl phosphate hydrolysis, 249, 70 reactions with two substrates, 249, 75-77 reversible reactions, 249, 77-78 with simple Michaelian enzyme, 249, 63-71 [fitting equations, 249, 63] with slow-binding inhibitors, 249, 88 with unstable enzymes, for kinetic characterization, 249, 85-89. 

A potent cysteine proteinase inhibitor PCPl 8.3 was isolated from potato tubers. The inhibitor has a broad inhibitor spectrum, including the bromelain enzymes, which am not inhibited by cystatin. PCPI shows a Ki value of 190 nM for stem bromelain, 33 nM for firuit bromelain, 0.06 nM for ananain, and 3.3 nM for papain [78]. ft is proposed (hat the differences of inhibitory spectrum between PCPl and the cystatins may be those of distinct supeifamilies of cysteine proteinase inhibitors. 

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