A FUNCTION FOR LIPOXYGENASE IN PROGRAMMED ORGANELLE DEGRADATION

Membrane-enclosed organelles, a defining characteristic of eukaryotic cells, are lost during differentiation of specific cell types such as reticulocytes (an intermediate in differentiation of erythrocytes), ce ntral fibre cells of the eye lens, and keratinocytes(1). The degradati on of these organelles must be tightly regulated with respect to both the time of activation and the specificity of membrane degradation. Th e expression of 15-lipoxygenase (15-LOX) peaks in reticulocytes immedi ately before organelle degradation(2). Here we show that 15-LOX integr ates into the membranes of various organelles, allowing release of pro teins from the organelle lumen and access of proteases to both lumenal and integral membrane proteins. In addition, by sparing the plasma me mbrane, 15-LOX shows the required specificity for organellar membranes . Thus, the action of 15-LOX provides a mechanism by which the natural degradation process can be explained. This conclusion is supported by our finding that lipoxygenase expression in the eye lens is restricte d to the region at which organelle degradation occurs.