The amino acid sequences of 301 glycosyl hydrolases and related enzymes have been compared. A total of 291 sequences corresponding to 39 EC entries could be classified into 35 families. Only ten sequences (less than 5% of the sample) could not be assigned to any family. With the sequences available for this analysis, 18 families were found to be monospecific (containing only one EC number) and 17 were found to be polyspecific (containing at least two EC numbers). Implications on the folding characteristics and mechanism of action of these enzymes and on the evolution of carbohydrate metabolism are discussed. With the steady increase in sequence and structural data, it is suggested that the enzyme classification system should perhaps be revised.

A classification of glycosyl hydrolases based on amino acid sequence similarities.

There are a number of components present in soybeans that exert a negative impact on the nutritional quality of the protein. Among those factors that are destroyed by heat treatment are the protease inhibitors and lectins. Protease inhibitors exert their antinutritional effect by causing pancreatic hypertrophy/hyperplasia, which ultimately results in an inhibition of growth. The lectin, by virtue of its ability to bind to glycoprotein receptors on the epithelial cells lining the intestinal mucosa, inhibits growth by interfering with the absorption of nutrients. Of lesser significance are the antinutritional effects produced by relatively heat stable factors, such as goitrogens, tannins, phytoestrogens, flatus-producing oligosaccharides, phytate, and saponins. Other diverse but ill-defined factors appear to increase the requirements for vitamins A, B12, D, and E. The processing of soybeans under severe alkaline conditions leads to the formation of lysinoalanine, which has been shown to damage the kidneys of rats. This is not generally true, however, for edible soy protein that has been produced under milder alkaline conditions. Also meriting consideration is the allergenic response that may sometimes occur in humans, as well as calves and piglets, on dietary exposure to soybeans.

Implications of antinutritional components in soybean foods

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/S0014-5793%2898%2901101-6

Deglycosylation of flavonoid and isoflavonoid glycosides by human small intestine and liver β-glucosidase activity

▪ Abstract The enzyme lactase that is located in the villus enterocytes of the small intestine is responsible for digestion of lactose in milk. Lactase activity is high and vital during infancy, but in most mammals, including most humans, lactase activity declines after the weaning phase. In other healthy humans, lactase activity persists at a high level throughout adult life, enabling them to digest lactose as adults. This dominantly inherited genetic trait is known as lactase persistence. The distribution of these different lactase phenotypes in human populations is highly variable and is controlled by a polymorphic element cis-acting to the lactase gene. A putative causal nucleotide change has been identified and occurs on the background of a very extended haplotype that is frequent in Northern Europeans, where lactase persistence is frequent. This single nucleotide polymorphism is located 14 kb upstream from the start of transcription of lactase in an intron of the adjacent gene MCM6. This change does...

Genetics of Lactase Persistence and Lactose Intolerance

Development of the Human Gastrointestinal Tract: A Review

1. In 32 human embryos, fetuses, newborns, and infants α-glycosidase activities (maltase, sucrase, isomaltase, palatinase, trehalase, dextranase, and amylase) and β-glycosidase activities (lactase and cellobiase) of the small intestine were determined. 2. The enzyme activities are distributed uniformly throughout the small intestine except in duodenum and terminal ileum. Lower values were found in these areas except for trehalase which remained high in the terminal ileum. 3. All glycosidases are present by the third month of intrauterine life. Most of the α-glycosidase activities reach maximal values by the 6th to 8th fetal month. Levels of activity are independent of the period lapsed since birth and independent of previous food intake. Only amylase and maltase 1 activities are low at birth in the full-term newborn. 4.β-glycosidase activities reach maximum values only at the end of normal gestation. After premature birth development of β-glycosidase activity occurs rapidly. 5. The observed development of the intestinal disaccharidases in the human is apparently different from that known in animals (calves, rabbits, pigs, and rats), where the α-disaccharidases develop only after birth and where lactase activity develops earlier in fetal life and drops after birth.

Intestinal glycosidase activities in the human embryo, fetus, and newborn.

Isolated intestinal lactase deficiency in the adult

1. No alpha-galactosidase activity in homogenates of human small intestinal mucosa was demonstrated either with stachyose, raffinose, or melibiose. 2. In a healthy child, oral raffinose and melibiose loads failed to produce changes in blood glucose, blood galactose, or red cell galactose-1-phosphate. Trace amounts of either saccharide were excreted in the urine. Following the raffinose load, diarrhea occurred and raffinose and melibiose as well as their hydrolysis products were found in the feces. 3. In a galactosemic patient, red cell galactose-1-phosphate rose as expected after ingestion of 2 gm of galactose. No such rise was seen after administration of equivalent and of double equivalent amounts of stachyose. Prolonged dietary supplementation with raffinose did not significantly alter non-fasting erythrocyte galactose-1-phosphate. 4. It is concluded that soybean formulas are generally safe for galactosemic infants; however, caution is advised for patients suffering from diarrhea.

S. Auricchio

Papers

Intestinal glycosidase activities in the human embryo, fetus, and newborn.

Isolated intestinal lactase deficiency in the adult

The handling of soya alpha-galactosides by a normal and a galactosemic child.

Disaccharidase activities in human intestinal mucosa.

Multiplicity of human intestinal disaccharidases. i. chromatographic separation of maltases and of two lactases.