All Three Isoforms of the Voltage-dependent Anion Channel (VDAC1, VDAC2, and VDAC3) Are Present in Mitochondria from Bovine, Rabbit, and Rat Brain

All three isoforms of the voltage-dependent anion channel (VDAC) were detected by immunoblot analysis of mitochondria isolated from rat, rabbit, and bovine brain. All three isoforms were associated with mitochondria after fractionation of rat brain extracts on sucrose density gradients. No VDAC isoforms were detected in non-mitochondrial fractions. Relative levels of the mRNAs coding the VDAC isoforms in rat, rabbit, and bovine brain were determined by RT-PCR. In all three species, the mRNA for VDAC2 was predominant. Relative to the mRNA for VDAC3, mRNAs for both VDAC1 and VDAC2 were more highly expressed in bovine brain than in rat brain. These results are consistent with the possibility that differences in relative expression of VDAC isoforms may be a factor in determining the species-dependent ratio of Type A:Type B hexokinase binding sites on brain mitochondria.