FIGURE 1.

Identification of MDH as an interacting protein with the bc₁ complex. A, SDS-PAGE analysis of bc₁ pulled-down proteins from matrix extract. Lanes 1-3, various amounts of MP as controls show the proteins in the matrix extract; lane 4, standard proteins; lanes 5 and 6, bc₁ complex and MP only as controls show the precipitates after centrifugation; lanes 7-9, shown is the bc₁ complex together with the pulled-down proteins from matrix extract. The solid arrow shows the main matrix protein being pulled down by the bc₁ complex. The dashed arrow shows some other bands being pulled down by the bc₁ complex. MP stands for mitochondrial matrix proteins; 1×, 3×, and 9× stand for 0.28, 0.83, and 2.50 mg/ml of MP in the experiment. PPT stands for precipitates. a, malate dehydrogenase; b, aspartate transaminase; c, unknown protein. B, shown are mass spectrometry spectra of protein sliced from SDS-PAGE gel. Spectrum data were collected from a MALDI-TOF mass spectrometer. It consisted of a series of multiple charged ions from each fragment on a mass-to-charge (m/z) ratio scale. 100% intensity represents the highest peak. C, shown is a Western blot analysis of bc₁ pulldown matrix proteins with anti-MDH antibody. Lane 1, purified bovine mitochondrial MDH; lane 2, mitochondrial matrix extract (MP); lane 3, bc₁; lane 4, the precipitate from dialyzed mixture of the bc₁ complex and mitochondrial matrix extract (bc₁+MP); lane 5, standard proteins.