The use of cation-bound microsomes for studies of protein synthesis

Low speed microsomes prepared by centrifuging at 30 times g for 10 minutes after interaction with Ca-2plus or Mg-2plus are comparable to high speed microsomes (105,000 times g) with respect to incorporation of 3-H-leucine in vivo, protein-synthesizing ability in vitro, and the pattern of ribosomal profiles on a linear sucrose density gradient. Low and high speed polyribosomes, i.e., those isolated with and without Ca-2plus or Mg-2plus from a postmitochondrial supernatant, also displayed similar protein-synthesizing capability in vitro and identical profiles on a linear sucrose density gradient. Other divalent cations, such as Ba-2plus, Ni-2plus, Co-2plus, Cu-2plus, Fe-2plus, Hg-2plus, Zn-2plus, and Sr-2plus, inhibited enzyme activities and depressed protein synthesis. Low speed microsomes may now be deemed suitable for all studies of microsomal function.