Proteolytic activity associated with the cell wall
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Abstract
As extracellular soluble proteins decreased during hypocotyl elongation, significant changes in the polypeptide pattern in the same protein fraction were observed, suggesting the presence of cell-wall-associated protease(s). Extracellular fluid (EF), containing water-soluble and cell wall-ionically bound proteins, was extracted from etiolated bean hypocotyls, and protease activity was measured at different pHs. Significant endopeptidase activity was observed at acidic pH, becoming maximal at pH 4.5. Moreover, an endopeptidase (EP) with a similar pH optimum was isolated from EF by affinity chromatography on haemoglobin-agarose gel. The isolated enzyme showed high thermal and temporal stability and dependence on metal cofactors. EP seems to be a monomeric enzyme with an apparent molecular mass of 52 kDa, capable of hydrolyzing several extracellular soluble polypeptides. Acidic EP activity increased during hypocotyl growth, reaching its highest value during the exponential phase of elongation, and then decreased. It is proposed that EP could be involved in the regulation of cell wall elongation.
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