Studies on the intestinal disaccharidases of the pigeon. III. Separation, purification and properties of sucrase-isomaltase and maltase-glucoamylase

Abstract

Sucrase-isomaltase (S-I) and maltase-glucoamylase (M-G) of the brush border have been purified to electrophoretic homogeneity from the pigeon small intestine. Heat-inactivated enzymes of crude homogenates of the pigeon intestinal mucosa, papain-solubilized enzymes and those obtained after chromatographic fractionation behaved in an identical manner. Depending on their sensitivity to heat treatment, the disaccharidases were identified to consist of two maltases; one, the heat-labile maltase, and the other, the heat-stable maltase. Sucrase and isomaltase constituted the thermolabile maltase and could be distinguished from each other. Maltase and glucoamylase formed the thermostable maltase the activities of which however, remained inseparable. Based on these results and in accordance with the nomenclature suggested by Dahlqvist & Telenius (1969), the pigeon intestinal disaccharidases were classified as follows: Maltase Ia = isomaltase, Maltase Ib = sucrase, and Maltase II = glucoamylase. DEAE-Cellulose chromatography did not resolve the two enzyme complexes but gel filtration of the active fractions recovered from the former step, resulted in their separation into two distinct peaks. Sucrase, isomaltase and a part of the maltase activity were recovered in the first peak which eluted close to the void volume. Glucoamylase and the remaining maltase activity were recovered in the second peak which appeared to have been retarded on the column because they were eluted much more slowly. The S-I and M-G complexes have an apparent molecular weight of 195 kd and 209 kd as determined by their gel-filtration pattern on Sepharose 6B. S-I hydrolysed alpha-glucosides such as maltose, sucrose and palatinose with a Km of 3.12 mM, 8 mM and 8.36 mM respectively and did not attack starch or dextran. In contrast, M-G catalysed the hydrolysis of starch, amylose and maltose with a Km of 3.12 mM, 7.59 mM and 3.52 mM respectively, and had no action on sucrose or palatinose. Both S-I and M-G were glycoproteins, and were inhibited by Ag+, Hg2+ and Tris but not by p-hydroxymercuribenzoate, iodoacetamide or imidazole. Na+ on the other hand activated both the enzyme complexes by about 20-25%. It is suggested that the molecular and catalytic properties of intestinal disaccharidases of pigeons do not differ considerably from those of Mammals.

Disaccharidases of Small‐Intestinal Mucosa

“…In some species the splitting into the two subunits may be incomplete or minimal (37,40; Hu C. et al, in preparation). In the case of the glucoamylase complex it also seems that one subunit only is anchored to the membrane directly (Hu C., et al, in preparation) via a hydrophobic segment apparently located not far from the N-terminal region of the polypeptide chain (41).…”

Duplications and Functional Convergence of Intestinal Carbohydrate-Digesting Enzymes

“…In many birds, including chickens, ostriches, and pigeons, two AGs have also been described (Prakash et al 1983;Hu et al 1987;Oosthuizen et al 1998). The fact that these avian enzymes exhibit properties similar to the better-known mammalian enzymes led to the hypothesis that the duplication of an ancestral a-glucosidase gene happened before the split of mammals and birds (Hu et al 1987), an assumption that has influenced many later studies (Karasov 2011;Karasov and Douglas 2013;Tamaoki et al 2016).…”