Action pattern, specificity, lytic activities, and physiological role of five digestive beta-glucanases isolated from Periplaneta americana.
Three laminarinases (LAM, LIC 1, and LIC 2) and two cellulases (CEL 1 and CEL 2) were purified to homogeneity from Periplaneta americana midguts. These beta-glucanases are secreted by salivary glands, stabilized by calcium ions, and have pH optima around 6. LAM (46 kDa) is active only on laminarin, native or with oxidized ends, and so it is an endo-beta-1,3-glucanase (EC 3.2.1.39). It processively releases mainly glucose from laminarin and shows lytic activity on fungal cells. LIC 1 (25 kDa) is an endo-beta-1,3(4)-glucanase (EC 3.2.1.6.), because it cleaves internal bonds on both laminarin and lichenin. LIC 1 lyses fungal cells and apparently have high affinity for sequences of cellotetraoses linked by beta-1,3 links, releasing cellotetraose from lichenin. The reaction catalyzed by LIC 1 is not in rapid equilibrium, as suggested by activity-pH data. These data also showed that a group in LIC 1 with pK=4.9 is necessary for substrate binding. LIC 2 (23 kDa) seems to be similar to LIC 1. The laminarinases are inactivated by carbodiimide, suggesting the presence of a carboxyl group involved in catalysis. LAM and LIC 2 are inhibited by excess laminarin as substrate. CEL 1 (72 kDa) and CEL 2 (73 kDa) quickly decrease the molecular weight of lichenin used as substrate. Therefore, they are endo-beta-1,4-glucanases (EC 3.2.1.4). Both CEL 1 and CEL 2 are also active on crystalline cellulose. The specificities of P. americana beta-glucanases agree with the omnivorous detritus-feeding habit of this insect, as they are able to attack plant (CEL 1, CEL 2, LIC 1 and LIC 2) and fungal (LIC 1 and LAM) cell walls.
Genta
Fernando A
FA
Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CP 26077, 05513-970, São Paulo, Brazil.
Terra
Walter R
WR
Ferreira
Clélia
C
D000818:Animals; D002234:Carbodiimides / Q000494:pharmacology; D002236:Carbohydrate Conformation; D002384:Catalysis; D044602:Cellulases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology*; D004064:Digestive System / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004795:Enzyme Stability; D005936:Glucans / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006867:Hydrolases / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D010526:Periplaneta / Q000201:enzymology*; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects; D012469:Salivary Glands / Q000201:enzymology; D013379:Substrate Specificity
D002234:Carbodiimides; D004791:Enzyme Inhibitors; D005936:Glucans; D011134:Polysaccharides; C008247:laminaran; D006867:Hydrolases; D044602:Cellulases; C015968:lichenin