Amylase action inhibitors

Several mono-carba-oligosaccharidic alpha amylase inhibitors, such as acarbose and its homologs, amylostatins, trestatins, oligostatins, adipo-sins, and so on, have been isolated from cultures of micro-organisms, and considerable interest in the biochemistry and chemistry of this class of inhibitors has been stimulated. The characteristic core-structure for inhibitory action is composed of a trihydroxy(hydroxymethyl)cyclohexene moiety and a 4-amino-4,6-dideoxy-D-glucopyranose moiety, bonded by way of an imino linkage at the allylic position. A similar structural unit has been found in the antibiotic validamycins. 

Kneen6354 reports that inhibitors obtained from cereal grains have different retarding effects upon the activity of bacterial and pancreatic amylases when examined under comparable conditions. These findings give further evidence for differences in the action of these alpha amylases. 

S. Ueda, Y. Koba, and H. Chaen, Action of amylase inhibitors produced by Streptomyces sp. on some carbohydrate hydrolases and phosphorylases, Carbohydr. Res., 61 (1978) 253-264. 

Uses Type 2 DM Action a-Glucosidase inhibitor delays digestion of carbohydrates Dose Initial 25 mg PO rid maint 50-100 mg rid (w/ 1st bite of each meal) Caution [B, —] Contra DKA, obst/inflammatory GI disorders SCr >2 mg/dL Disp Tabs SE Flatulence, D, abd pain Interactions T Effects W/ celery, coriander, juniper berries, ginseng, garlic X- effects W/ENH, niacin, intestinal absorbents, amylase, pancreatin X- effects OF digoxin, propranolol, ranitidine EMS Can X- digoxin level-monitor ECG in pts on digoxin therapy OD May cause severe adverse GI Sxs symptomatic and supportive... 

The antagonism of GA action by ABA can be seen in studies of steady-state mRNA accumulation in aleurone cells, a major site of a-amylase synthesis in germinating cereal seeds (Fig. 3). GA treatment promotes the accumulation of high levels of a-amylase, shown by immunoprecipi-tation, while ABA, alone or with GA, completely represses this accumulation. In contrast, ABA clearly promotes the accumulation of a-amylase inhibitor mRNA, as determined by specific immunoprecipi-tation, while GA alone slightly reduces the level of a-amylase inhibitor mRNA. However, GA, together with ABA, does not decrease the level... 

The mechanism of action of abscisic acid (ABA) has been studied to the greatest extent in the barley aleurone system (29), in which ABA counteracts the effect of GA in the induction of hydrolases. This action of ABA has largely been the basis for speculating that ABA may act specifically to inhibit, by some unknown mechanism, DNA-dependent RNA synthesis. Much evidence indicates that ABA acts at the transcriptional level, but it also has been proposed that the inhibition of induction of a-amylase synthesis is caused, at least in part, by an effect on translation because ABA still inhibited the formation of a-amylase at 12 hr when cordycepin (an inhibitor of RNA synthesis) no longer had an effect (30). 

In the body, enzymes are compartmentalized and function under highly restricted conditions. Some enzymes (e.g., proteinases) are not substrate-specific. When present in active form in an inappropriate part of the body, they act indiscriminately and cause considerable damage to the tissue. Inhibitors inactivate these enzymes at sites where their action is not desired. Proteinase inhibitors, which are themselves proteins, are widely distributed in intracellular and extracellular fluids. Protein inhibitors of enzymes other than proteinases are relatively rare. Such inhibitors are available for a-amylases, deoxyribonuclease I, phospholipase A, and protein kinases. 

Product Inhibition. In most microbiological and biochemical systems accumulation of end products exercises an inhibitory effect on the rate of the forward reaction. Stimulation by end product is thermodynamically improbable. One of the major products of hydrolysis of cellulose is cellobiose. There is a stimulation by cellobiose of Cx activity of Streptomyces spp. filtrates only when the substrate is solubilized by the introduction of various substituents—e.g., CMC, hydroxycellulose, cellulose acetate, etc. Stimulation is absent when unsubstituted cellulose is used (14). On the other hand, product inhibition is common. Cellobiose inhibits the hydrolysis of cellulose by filtrates of most of the 36 organisms tested. This action of cellobiose is believed to be that of an end product inhibiting an enzymatic hydrolysis in much the same manner that maltose inhibits hydrolysis of starch by a-amylase. The inhibitory effect of products varies with the organism from which the cellulase is derived. Thus, lactose is a very good inhibitor of the enzyme from... 

Recently, a semisynthetic deoxynorjirimycin derivative Bay o 1248 (20), which is absorbed from the intestine and does not produce carbohydrate malabsorption, was reported as a potent glucosidase inhibitor exhibiting strong sucrase and maltase inhibitory activity and no amylase inhibition. Administration of which has a longer duration of action than acarbose, reduces food intake, body weight gain and epididymal fat pad weight in rats. ... 

In summary, our present knowledge of the mechanism of action of the red kidney bean a-amylase inhibitor indicates that an initial complex is formed between inhibitor and enzyme which does not involve the active site of the enzyme (complex still fully active). Subsequently, there is a conformational change in the complex which destroys the ability of a-amylase to hydrolyze large substrates but does not prevent their binding to the enzyme. 

A large amount of amylase inhibitors, of at least four kinds, were produced by Streptomyces sp. No. 280 when cultivated on 3% oatmeal medium and it was found that the molecular weight of the inhibitors were transformed to small molecules during the cultivation time. The transformation of the amylase inhibitor was found to result from degradation of its carbohydrate moiety by a-amylase in the culture broth. The amylase inhibitor was hydrolysed partially by the action of Taka-amylase A or hog pancreatic a-amylase. With hydrolysa-tion of amylase inhibitor by a-amylase, neutral sugars (mainly maltose) were... 

Fig. 3. Effect of the transcription inhibitor, cordycepin, on the action of ABA in barley aleurone layers. Northern blot analysis is the same as described under Fig. 2. Aleurone layers were incubated for 25 h in the absence of GA3 (lane 7), 25 h in the presence of lO M GA, (lane 2), 24 h in the presence of GA, and 2 X lO M ABA with a second addition of ABA at 12 h (lane i), 25 h in the presence of GA3 with ABA added 10 h after GA3 (lane 4), 25 h in the presence of GA3 with ABA added 20 h after GA3 (lane 5), or 25 h in the presence of GA3 with ABA and 10 " M cordycepin added 20 h after GA3 (lane 6). Note that cordycepin addition prevented the reduction of a-amylase mRNA induced by ABA (cf lanes 5 and 6). From Nolan et al. [19]...

Several models have been proposed to account for the non-random distribution of oligosaccharides formed when polysaccharides are hydrolysed by a-amylase. The preferred-attack model assumes that the probability of bond-cleavage depends on the position of the bond in the chain the repetitive (or multiple-attack) model assumes that a-amylase can form a cage-like complex with the substrate and attack it several times during a single encounter the multiple-enzyme (or dual-site) model assumes that the substrate is hydrolysed by the combined actions of exo- and en /o-enzymes. The effects of pH, inhibitors, and the chain length of the substrates have been studied in an attempt to decide which of the three models best fits the action of a-amylase. The effects of these variables on either the distribution of products or the action pattern of the enzyme were incorporated into the models, which were then used to interpret experimental data obtained with porcine pancreatic a-amylase. 

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