Biosynthesis of leupeptin IV. Is protein turnover in leupeptin producer cells affected by leupeptin?.

There was no significant difference between the rates of protein degradation in cells of a leupeptin-producing strain and that of a leupeptin-nonproducing strain, the latter being derived from the former by mutation. Protein autodigestion in a cell homogenate of the leupeptin producer was sensitive to EDTA and chymotrypsin and less sensitive to leupeptin. On the contrary, protein degradation caused by exogenous trypsin in a similar homogenate was highly sensitive to leupeptin. A labeling experiment with [14C]-arginine of a culture of the leupeptin producer strain revealed that leupeptin was accumulated mostly in the medium and only slightly in the cells; the ratio between the amount in the medium and that in the cells was about 250:1. In contrast, leupeptin acid, the proximal intermediate having no antiplasmin activity, showed a ratio of 5:1.