Presence of Serine Enzymes in Endoplasmic Reticulum of Spinach Callus

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Two serine enzymes were detected in microsomes of spinach callus by labeling with [^3H]-di-isopropyl phosphorofluoridate (DFP) and examination by SDS-polyacrylamide gel electrophoresis. The contents of the larger (mol wt 44,000) and the smaller (mol wt 39,000) DFP-binding protein (proteins which have a DFP-reactive site) were maximum at the third and the second week after cell inoculation, respectively. The positions of both proteins on the continuous sucrose gradient coincided with that of NADH-cytochrome c reductase, a marker enzyme of the endoplasmic reticulum. The smaller protein was released from microsomes treated with 0.05% deoxycholate. The larger protein was solubilized with 0.5% cholate, but not with 0.05% deoxycholate, and the apparent molecular weight of the solubilized protein was about 90,000 in 0.5% cholate on Sephacryl S-200 column. [^3H]-DFP-binding with the larger protein was strongly inhibited by DFP, phenylmethylsulfonyl fluoride, N-p-tosyl-L-Iysine chloromethyl ketone and L-1-tosylamide-2-phenylethyl chloromethyl ketone, and slightly by p-chloromercuric benzoate and o-phenanthroline. DFP binding with the smaller one was strongly inhibited by DFP and PMSF, but not by other reagents.
日本植物生理学会の論文