
TY  - JOUR
A1  - Ramos, PCR 
A1  - Cordeiro, ACF 
A1  - Ferreira, RMB 
A1  - Ricardo, CPP 
A1  - Teixeira, ARN 
T1  - The Presence of Ubiquitin-Protein Conjugates in Plant Chloroplast Lysates Is Due to Cytosolic Contamination
JF  - Functional Plant Biology
JO  - Functional Plant Biol.
Y1  - 1995
VL  - 22
IS  - 6
SP  - 893
EP  - 901
KW  - 
UR  - https://doi.org/10.1071/PP9950893 
N2  - Chloroplasts were isolated by Percoll density gradient centrifugation from Lemna minor and Spinacia oleracea grown under normal conditions or from L. minor subjected to sulfur starvation, a condition that induces a dramatic increase in the rates of proteolysis, namely in the degradation of the chloroplast enzyme ribulosebisphosphate carboxylase. The presence of free ubiquitin or ubiquitin-protein conjugates was not immunologically detected in the purified chloroplast extracts under either of these conditions. Moreover, no ATP-dependent conjugation of 125I-labelled ubiquitin to endogenous proteins was detected in L. minor chloroplast lysates. Our results support the view that plant chloroplasts do not possess free ubiquitin or ubiquitin conjugating activity. Furthermore, treatment of the mechanically isolated chloroplasts with thermolysin suggests that the presence of ubiquitin-protein conjugates in some chloroplast preparations is due to cytosolic contamination. 
ER  -

