β-Mannoside mannohydrolase and the mobilization of the endosperm cell wall of lettuce seeds, cv. Grand Rapids.

Mobilization of the endosperm cell-wall reserves of Lactuca sativa L. cv. Grand Rapids requires endo-β-mannanase and α-galactosidase activity. A third enzyme, β-mannoside mannohydrolase (EC 3.2.1.25) is also involved. We have determined the optimum extraction and assay conditions for this enzyme, which is soluble only in high-salt (1 M NaCl) buffer. It is located exclusively within the cotyledons, in association with a cellulosic cell-wall fraction. Its substrates are the products of endosperm cell-wall mobilization, mannobiose and mannotriose, which diffuse to the cotyledons and are hydrolyzed extracellularly by the β-mannoside mannohydrolase.