CYTOSOLIC ASPARTATE-AMINOTRANSFERASE ENCODED BY THE AAT2 GENE IS TARGETED TO THE PEROXISOMES IN OLEATE-GROWN SACCHAROMYCES-CEREVISIAE

Fatty acid beta-oxidation in peroxisomes requires the continued uptake of fatty acids or their derivatives into peroxisomes and export of be ta-oxidation products plus oxidation of NADH to NAD. In an earlier stu dy we provided evidence for the existence of an NAD(H) redox shuttle i n which peroxisomal malate dehydrogenase plays a pivotal role. In anal ogy to the NAD(H)-redox-shuttle systems in mitochondria we have invest igated whether a malate/aspartate shuttle is operative in peroxisomes. The results described in this paper show that peroxisomes of oleate-g rown Saccharomyces cerevisiae contain aspartate aminotransferase (AAT) activity. Whereas virtually all cellular AAT activity was peroxisomol in oleate-grown calls, we found that in glucose-grown cells most of t he AAT activity resided in the cytosol. We demonstrate that the gene A AT2 codes for the cytosolic and peroxisomal AAT activities. Disruption of the AAT2 gene did not affect growth on oleate. Furthermore beta-ox idation of palmitate was normal. These results indicate that AAT2 is n ot essential for the peroxisomal NAD(H) redo shuttle.