Ranitidine induces inhibition and structural changes in sucrase

Metformin-Induced Invertase Unfolding: Enzyme Kinetics and Activity Regulation

The effects of metformin on invertase activity and its inhibition on sucrose digestion were studied. The rapid unfolding kinetics of invertases, followed a two-state model with an inactive intermediate formation. The dynamic interaction between metformin and invertase caused the secondary structure of the enzyme to become less β-sheet, more α-helix, and random coiling oriented, which weakened the binding force between enzyme and its substrate. Metformin acted as a chaotrope and disrupted the hydrogen bonds of water, which facilitated the unfolding of invertase. However, some sugar alcohols, which promoted the H-bond formation of water, could repair the secondary structure of metformin-denatured invertase and therefore regulate the enzyme activity. This research enriches our understanding of the mechanism of enzyme unfolding induced by guanidine compounds. Moreover, because metformin and sugar substitutes are of concern to diabetes, this research also provides useful information for understanding the activity of the digestive enzyme that coexists with metformin and sugar alcohols.

[Enteropathy with impaired membrane digestion and the prospects for cytoprotective therapy]

The article describes enteropathy with impaired membrane digestion (EIMD) as a new nosological form. The main clinical manifestation of EIMD is the poor tolerance of food products, in particular carbohydrates and a decrease in the activity of membrane enzymes, in particular, carbohydrates, in the mucous membrane of the small intestine. The cause of the disease can be acute intestinal infections, viruses, drugs and other agents that damage the small intestine. The pathophysiology, clinical picture and diagnosis of EIMD are described. The basis of therapy is rebamipide, which has the ability to reduce the symptoms of carbohydrate intolerance and increase the activity of disaccharidases.

蔗糖酶-异麦芽糖酶缺乏与腹泻的研究进展

蔗糖酶-异麦芽糖酶(sucrase-isomaltase, SI)是蔗糖酶在肠道内最主要的存在形式, 是最丰富的肠道二糖酶, 其包含了所有的蔗糖酶活性, 大部分的异麦芽糖酶活性及60%-80%的麦芽糖酶活性. 蔗糖酶-异麦芽糖酶缺乏症(sucrase-isomaltase deficiency, SID)是由于该二糖酶缺乏导致二糖吸收不良, 肠道正常生理功能受损, 机体营养不良, 生长发育落后, 甚至产生危及生命的胃肠道症状. 其最主要的临床表现是腹泻. 临床上通过调整肠道SI活性来治疗腹泻, 并将SI活性用于临床诊断. 本文主要阐述SID与腹泻的关系、研究进程以及诊疗手段, 促进SI在药理方面的研究.

The multiple roles of sucrase-isomaltase in the intestinal physiology

Osmotic diarrhea and abdominal pain in humans are oftentimes associated with carbohydrate malabsorption in the small intestine due to loss of function of microvillar disaccharidases. Disaccharidases are crucial for the digestion and the subsequent absorption of carbohydrates. This review focuses on sucrase-isomaltase as the most abundant intestinal disaccharidase and the primary or induced pathological conditions that affect its physiological function. Congenital defects are primary factors which directly influence the transport and function of sucrase-isomaltase in a healthy epithelium. Based on the mutation type and the pattern of inheritance, a mutation in the sucrase-isomaltase gene may exert a variety of symptoms ranging from mild to severe. However, structure and function of wild type sucrase-isomaltase can be also affected by secondary factors which influence its structure and function either specifically via certain inhibitors and therapeutic agents or generally as a part of intestinal pathogenesis, for example in the inflammatory responses. Diagnosis of sucrase-isomaltase deficiency and discriminating it from other gastrointestinal intolerances can be latent in the patients because of common symptoms observed in all of these cases.

Here, we summarize the disorders that implicate the digestive function of sucrase-isomaltase as well as the diagnostic and therapeutic strategies utilized to restore normal intestinal function.

Effect of cimetidine on catalase activity of Pseudomonas aeruginosa: a suggested mechanism of action

Catalase is an important enzyme for the degradation of hydrogen peroxide in cells. Bacteria have potent catalase to deal with H2O2 in their medium culture. Any chemicals that inhibit catalase activity can be harmful for cells. Histamine H2 antagonist drugs such as cimetidine and ranitidine are used for the treatment of gastrointestinal tract disorders. The present results showed that cimetidine could inhibit the catalase activity of Pseudomonas aeruginosa in a competitive inhibition. The determination of IC50 value and Ki (6.5 μM) of cimetidine demonstrated that the enzyme binds to the drug with high affinity. Binding of the drug to the enzyme was pH-dependent and no binding was observed at basic pH (>9) and acidic pH (<6). Moreover, the imidazole ring and cyanoguanidine group of cimetidine may play an important role in inhibition by binding to Fe in heme group and glutamic acid 51 residue on the enzyme, respectively. Ranitidine had no effect on the catalase activity.