Hydrolyzes 1,4-beta linked polysaccharide backbones of mannans. Has high activity toward locust bean gum (PubMed:18579426, PubMed:25082572). Also active toward konjac and beta-1,4-mannan. Hydrolyzes mannotetraose (M4) and mannopentaose (M5) to mannobiose (M2) and mannotriose (M3) with a little production of mannose (M1). Hydrolyzes beta-1,4-mannan to M2, M3 and M4. Hardly hydrolyzes M2 and M3. Does not hydrolyze p-nitrophenyl-beta-D-mannopyranoside, gua-gum, carboxymethyl cellulose, soluble starch or laminarin (PubMed:18579426). Random hydrolysis of (1->4)-beta-D-mannosidic linkages in mannans, galactomannans and glucomannans. Activated particularly by Ca(2+) and Zn(2+), and to a lesser extent by Na(+), K(+), Mg(2+) and Cu(2+). Activation effect of the divalent metal ions Ca(2+), Zn(2+), Mg(2+) and Cu(2+) is reduced significantly by the addition of EDTA. Strongly inhibited by Mn(2+), Hg(2+) and Ag(+). kcat is 1659.90 sec(-1) for 0.5% locust bean gum (at pH 3.5 and 10 degrees Celsius in the presence of 50mM sodium citrate). Optimum pH is 3.5. Maintains more than 50% of the maximum activity at pH 2.5-6.0. Not active at a pH above 7.0. Optimum temperature is 30 degrees Celsius. Retains approximately 20-40% of its maximum activity even at 0-5 degrees Celsius. Drastic loss of activity at temperatures above 45 degrees Celsius, at which the half-life of the enzyme activity is less than 10 min. Monomer. Potential use in mannan-hydrolysis industries which need especially low temperature and an acidic condition such as the food and the animal feed industries. Belongs to the glycosyl hydrolase 5 (cellulase A) family.