Studies on the insulin-degrading activity of rat liver plasma membranes.

Golgi preparation. Lactose/glycylglycine eluted a few proteins, especially one of about 70000mol.wt. NaCl eluted several further proteins of group B, of mol.wt. 67000-76000, as well as several proteins of groups C and D. The EDTA extract contained several proteins present in the NaCl extract, but was different from the NaCl extract in that it usually contained three proteins of mol.wts. 38000, 40000 and 43000. The major components extracted from group D had mol.wts. near 25000, whereas the NaCl extract contained proteins from the 32000mol.wt. region. The use of polyacrylamide gradient gels described achieves good resolution of Golgi-membrane preparations into separate components. Although a large number of bands of material are seen, the pattern is very reproducible. The great enrichment of galactosyltransferase suggests that much of the pattern reflects the composition of Golgi membranes themselves, although a contribution by contaminant membranes must be expected. Other reports have implied a similarly complex pattern for Golgi membranes (Keenan & Huang, 1972; Oda et al., 1979).