Brush Border Enzymes
Brush border enzymes are the major constituents of detergent-insoluble complexes of the small intestinal mucosa. Brush border enzymes include aminopeptidase N, transmembrane sucrase-isomaltase, and GPI-anchored alkaline phosphatase. They comprise 25 to 30 percent of the total protein in glycolipid microdomains. The brush border enzymes are prominent, and the only major protein band missing is one of 36 kDa. The presence of the Galectin-4 antibody confirms the central position of brush border enzymes.
The pig’s small intestinal mucosal mucus contains abundant transmembrane brush border enzymes, including galectin-4. This enzyme is an animal lectin lacking the N-terminal signal peptide and forms distinct soluble clusters. The lectin is localized to the rootlets of microvillar actin filaments. It binds to glycolipids in the intestinal wall and maybe a natural ligand for galectin-4.
These enzymes are brushed border proteins and have a cytoplasmic tail and large glycosylated ectodomains. These brush border proteins associate with the membrane of enterocytes and have been found in association with small blisters. Moreover, galectin-4 was associated with microvilli, suggesting that it is a brush border enzyme. The brush border membrane has been shown to enrich galectin-4 five to ten times over the homogenate.
In human galectin-4N, the N-terminal CRDs are linked together by variable-length linker regions. This CRD region is likely to exhibit distinct binding preferences. Since these proteins are important in many disease states, their interest has increased significantly. These findings also suggest that they play a role in various physiological conditions. However, their mechanisms remain unclear. While they may act as a signal for the immune system, it is not yet known how galectins work.
Glycosamines are a primary substrate of galectin-4. Glycosphingolipids are a major component of lipid rafts, and galectin-4 is a key player in recruiting apical glycoproteins into DRMs. Moreover, the high density of N-glycans in rafts supports galectin-4’s affinity for these raft-associated glycoproteins.
The four disaccharidases involved in the digestion of carbohydrates are found in the brush border membrane of the intestinal crypt and adenoma. The three other enzymes, maltase-glucoamylase and sucrase-isomaltase are also present in the brush border membrane. A deficiency of maltase-glucoamylase causes an osmotic pull on the fluid in the abdomen, loose stools, and abdominal cramping.
Maltese-glucoamylase is 2% of the brush border protein and is an essential enzyme in the absorption of sugars. It is responsible for cleaving small glucose polymers. It is a noncompetitive inhibitor of a-amylase and has a role in regulating the activity of luminal a-amylase. Besides maltase, other brush border enzymes are lactase and sucrase.
Maltase-glucoamylase, or MGA, is a two-subunit glycosidase that hydrolyzes linear alpha-1,4-linked oligosaccharides. It plays a key role in glucose production in the human lumen and is a potential drug target. The MGAM subunits have different substrate specificities and function as brush border enzymes.
Maltase-glucoamylase is the last step in starch digestion in the small intestine. It is found in the same family of genes as SI. MGAM and SI complement each other and function in different ways. Both enzymes have two identical catalytic sites. A reduction in maltase-glucoamylase activity is associated with a reduced incidence of CSID. In contrast, normal small bowel histology is required to diagnose the disease.
Small intestinal brush borders have a unique composition of proteins. They are highly abundant in transmembrane brush border enzymes such as aminopeptidase N. They are also GPI-anchored and constitute an estimated 25-30% of the total protein in glycolipid microdomains. The brush border contains only one major protein band, 36 kDa, recognized by an antibody raised against galectin-4.
In this study, we examined the properties of aminopeptidase N, which hydrolyzes L-phenyl-L-alanine in the brush border, as compared with its counterparts in the cytosol. Our results showed that the brush border enzymes were almost entirely localized within the brush border of the villi. Furthermore, they were nearly completely resistant top-hydroxymercuribenzoate, whereas those that hydrolyze L-leucine were only partially resistant to heating.
Aminopeptidase N has been associated with the microvillar cytoskeleton, suggesting that they act as natural ligands for galectin-4. Aminopeptidase N exhibits lactose-resistant clustering, which may be related to its association with the microvillar cytoskeleton. The protein is also clustered with an actin-like 42-kDa band in the bottom fraction of the gradient.
Aminopeptidase N is located within the midgut brush border membrane of Bombyx mori. Its main role is to hydrolyze N-terminal amino acids of peptides and generate dipeptides. Its activities are correlated with tumor load. It is also thought to play a role in angiogenesis. Its high expression in cancer cells is strongly associated with the presence of tumors, suggesting a role for the enzyme in tumor growth.
Intestinal alkaline phosphatase (IALP) is a brush border enzyme that regulates the intestinal surface pH and plays a role in fatty acid absorption. It plays a pivotal role in intestinal microbial homeostasis by dephosphorylating lipopolysaccharide, a type of lipid. Isolated exogenous IAP is a potential therapeutic agent for gut barrier dysfunction, as it exerts anti-inflammatory activity.
Experiments using knockout mice demonstrated that fat absorption lowered the rate of IAP transport through enterocytes. This suggests that IAP affects lipid flow through the Golgi complex, a major hub of cellular membrane trafficking. Endocytosis of IAP after fat absorption would affect the overall membrane dynamics of the enterocyte, resulting in slower basolateral secretion.
Human intestinal alkaline phosphatase has a low Km value at physiological pH. Phosphate, vanadate, and arsenate inhibit alkaline phosphatase at physiological pH. Furthermore, alkaline phosphatase activity in brush border membrane ves was augmented by basal delivery of nutrients. Moreover, basal delivery of nutrients promoted Caco-2 proliferation.
While IAP is a natural intestinal brush border enzyme, it is still unclear how it contributes to aging. Its role in maintaining intestinal microbiome homeostasis and preserving the gut barrier function may require more investigation. In the meantime, oral IAP supplementation may be a novel strategy for preventing age-related diseases in humans. Counteracting the chronic inflammatory state that contributes to frailty could help avoid many conditions associated with aging.
A brush border enzyme is one of several kinds of digestive enzymes. These enzymes break down starches and disaccharides. The different brush border enzymes include lactase, maltase, and isomaltase. These enzymes are found in the small intestine. Lactose is the most abundant brush border enzyme in human and animal digestive systems.
In the small intestine, lactase is a brush-border enzyme produced by a group of cells called lactase. This brush-border enzyme breaks down lactose into smaller sugars, glucose, and galactose. Lactose is also found in milk and other foods containing milk sugars, and a lack of it can cause symptoms of lactose intolerance, gas, and bloating.
The other lactose-breaking enzyme is known as platinize. Both of these enzymes break down glucose and fructose. Moreover, sucrase is the most important digestive enzyme for milk. Without it, the digestive system cannot absorb enough nutrients from food. So, it compensates for this lack by breaking down glucose. When lactose is broken down, it is converted into two molecules of glucose and fructose.
A primary type of lactase deficiency occurs when lactase levels fall too low. The activity of brush-border lactase begins to rise in late fetal life and peaks between three months and one year. The level gradually decreases with age. Although the period of brush-border lactase varies in different ethnic groups, it is consistent with the general decline in lactase in adulthood.
A recent study evaluated the relationship between lycopene and brush border enzymes in gastrointestinal tract cancer patients. Five Fu was administered intraperitoneally in the control group, and lycopene was given to the 5-Fu group. After treatment, the brush border enzyme activities were determined, and histopathological analyses were performed. Protein expression of apoptotic marker genes was also measured by western blotting. Moreover, supplemental lycopene decreased Cox-2 expression and increased brush border enzyme activities.
The intestinal brush border membrane lines the lumen of the gut and is vital for digestion and absorption of nutrients. Alterations in the activities of brush border bound marker enzymes in chemotherapy patients indicate damage to the intestinal brush border membrane. This has been observed for various toxic compounds, including lycopene. Hence, it is vital to understand the relationship between lycopene and brush border enzymes. In addition to their beneficial effects, brush border enzymes have also been linked to other health benefits.
The antioxidant activity of lycopene is dependent on its isomerization. The isomerization process of lycopene alters the peak height. Therefore, lycopene concentration in the serum can be measured using the peak area measurement. Using a Waters 490 programmable multiwavelength detector with four channels, this measurement was performed. A peak height measurement was taken for all carotenoids and vitamins, except lycopene.