Wynn R M, Kochi H, Cox R P, Chuang D T
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235.
Biochim Biophys Acta. 1994 Sep 28;1201(1):125-8. doi: 10.1016/0304-4165(94)90161-9.
The N-terminal sequences of the E1 alpha, E1 beta and E2 subunits of the human branched-chain alpha-keto acid dehydrogenase complex have been determined by microsequencing. The N-terminal of human E1 beta and E2 subunits (Val and Gly, respectively) are identical to those of the corresponding rat and bovine subunits. However, the N-terminus of the human E1 alpha subunit (Ser) is identical to bovine, but differs from the rat E1 alpha (Phe) subunit. Comparison of the N-terminal sequences of human and rat E1 alpha subunits shows that the serine residue at the +1 position in the human sequence is replaced by a proline residue in the rat sequence. The presence of the proline residue apparently causes a 5'-shift by one residue in the cleavage site by the mitochondrial processing peptidase in the rat sequence, when compared to the human sequence. The results provide evidence that the mitochondrial processing peptidase cannot cleave an X-Pro bond, similar to trypsin, chymotrypsin and microsomal signal peptidases.
通过微量测序确定了人支链α-酮酸脱氢酶复合体E1α、E1β和E2亚基的N端序列。人E1β和E2亚基的N端（分别为缬氨酸和甘氨酸）与相应的大鼠和牛亚基相同。然而，人E1α亚基的N端（丝氨酸）与牛的相同，但与大鼠E1α（苯丙氨酸）亚基不同。人和大鼠E1α亚基N端序列的比较表明，人序列中+1位的丝氨酸残基在大鼠序列中被脯氨酸残基取代。与人类序列相比，脯氨酸残基的存在显然导致大鼠序列中线粒体加工肽酶切割位点的5'端移位一个残基。结果提供了证据，表明线粒体加工肽酶不能切割X-脯氨酸键，类似于胰蛋白酶、胰凝乳蛋白酶和微粒体信号肽酶。
