HUMAN COMPLEX-II (SUCCINATE-UBIQUINONE OXIDOREDUCTASE) - CDNA CLONINGOF THE FLAVOPROTEIN (FP) SUBUNIT OF LIVER-MITOCHONDRIA

Complex II (succinate-ubiquinone oxidoreductase) is an important enzym e complex in both the tricarboxylic acid cycle, and the aerobic respir atory chains of mitochondria in eukaryotic cells and prokaryotic organ isms. In this study, homology probing with mixed primers for the polym erase chain reaction and subsequent sequence analysis were successfull y applied to clone cDNA for the flavoprotein (Fp) subunit of human liv er complex II. The isolated clone contains an open reading frame of 1, 992 nucleotides and encodes a mature protein of 621 amino acids with a molecular weight of 68,011. The amino acid sequence was highly homolo gous with that of bovine heart Fp (93.2%) and was quite different from the partial sequence of human placental Fp reported previously [Malco vati et al. (1991) in Flavins and Flavoproteins 1990, pp. 727-730], wh ich showed striking homology to that of Bacillus subtilis. To solve th is discrepancy, the partial cDNA sequences of the stomach and placenta l Fp subunits of human complex II were determined in addition to the f ull length cDNA of liver. The sequence data, sensitivity to thiol reag ents and antigenic properties indicated that the major form of Fp subu nit in human complex II is unique at least among the three tissues ana lyzed, and is more similar to the Fp subunit of bovine heart than to t hat of B. subtilis.