Inducer of pectic acid lyase in Erwinia carotovora

Abstract

PECTIC acid (polygalacturonic acid) lyase (EC 4.2.2.2., PAL) formed in bacteria, catalyses the transeliminative cleavage of pectic acid¹. Because PAL both macerates plant tissues and causes cell leakage and death^2,3, it has often been investigated biochemically from the industrial and plant pathological point of view. Physiological studies, however, have been limited, probably because PAL is in part an extracellular enzyme⁴. Thus most studies of its inducibility have compared activities in filtrates of cells cultured on different carbon sources^5,6. But assay of an extracellular enzyme does not necessarily reveal changes in its rate of synthesis. In Erwinia carotovora, however, the PAL that can be purified from cell-free extracts is probably the same protein as the extracellular enzyme¹. In strain EC-1 of E. carotovora, non-induced PAL activity is three to four times greater in cell-free extracts than in the culture filtrate during log phase growth, and the relative rate of increase of intracellular enzyme activity after induction is 130 times greater than the rate of release of PAL into the culture filtrate (unpublished data). I therefore used this strain to study induction by measuring PAL activities in cell-free extracts. I report here that the inducer of PAL in E. carotovora may not be pectic acid itself but its breakdown product.