Generally the formation of native disulphide bond is essential for the folding and maturation of proteins in the secretory pathways.These bonds are formed in the rough E.R, and also in the intramembrane of the mitochondria.
Basically an oxdative parthways is required for the disulfide bond to form, while a reductive pathway is needed for the formation of isomers for non-native disulphide bonds. These oxidative pathways takes place in the rE.R
Generally the disulphide bonds is usually formed by oxidation of two cysteines bonds. it does not occur in the cytoplasm because it is always in reduced state due to the presence of disulphide reductase. The same explains why it does not occur in the Nuclei
