Synthesis of a dicyclohexylcarbodiimide-binding proteolipid by cucumber (Cucumis sativus L.) mitochondria.

When isolated cucumber (Cucumis sativus L.) mitochondria were treated with (14)C-labelled dicyclohexylcarbodiimide (DCCD), a single polypeptide was predominantly labelled. This polypeptide was soluble in 1-butanol or chloroform: methanol (2: 1, v/v) and had an apparent molecular mass of approximately 7 kDa; it therefore had the characteristic properties of the DCCD-binding proteolipid subunit of the ATP synthase complexes of mitochondria, chloroplasts, and prokaryotes.When isolated cucumber mitochondria were allowed to synthesize protein in the presence of [(35)S]methionine and then extracted with 1-butanol or chloroform: methanol (2: l, v/v), a (35)S-labelled proteolipid that migrated more rapidly on SDS-polyacrylamide gels than the pro-teolipid labelled by [(14)C]DCCD was solubilized. Treatment of mitochondria with unlabelled DCCD after they had been allowed to synthesize protein, specifically converted some of the [(35)S]methionine-labelled proteolipid to a form that comigrated with the [(14)C]DCCD-labelled proteolipid. We therefore conclude that a DCCD-binding proteolipid is synthesized by isolated cucumber mitochondria.