Cytosolic Aspartate Aminotransferase Encoded by the AAT2 Gene is Targeted to the Peroxisomes in Oleate-Grown Saccharomyces Cerevisiae

Authors


R. J. A. Wanders, Academic Medical Center, University of Amsterdam, Department of Clinical Biochemistry (FO-224), P.O. Box 22700, NL-1100 DE Amsterdam, The Netherlands
Fax:+31 20 6962596.
E-mail:wanders@amc.uva.nl

Abstract

Fatty acid β-oxidation in peroxisomes requires the continued uptake of fatty acids or their derivatives into peroxisomes and export of β-oxidation products plus oxidation of NADH to NAD. In an earlier study we provided evidence for the existence of an NAD(H) redox shuttle in which peroxisomal malate dehydrogenase plays a pivotal role. In analogy to the NAD(H)-redox-shuttle systems in mitochondria we have investigated whether a malate/aspartate shuttle is operative in peroxisomes. The results described in this paper show that peroxisomes of oleate-grown Saccharomyces cerevisiae contain aspartate aminotransferase (AAT) activity. Whereas virtually all cellular AAT activity was peroxisomal in oleate-grown cells, we found that in glucose-grown cells most of the AAT activity resided in the cytosol. We demonstrate that the gene AAT2 codes for the cytosolic and peroxisomal AAT activities. Disruption of the AAT2 gene did not affect growth on oleate. Furthermore β-oxidation of palmitate was normal. These results indicate that AAT2 is not essential for the peroxisomal NAD(H) redox shuttle.

Abbreviations.
AAT

aspartate aminotransferase

CTAI

peroxisomal catalase

HAD

3-hydroxyacyl-CoA dehydrogenase

MDH

malate dehydrogenase

PGK

phosphoglycerate kinase

SDH

succinate dehydrogenase

PTS

peroxisomal targeting sequence

PGI

phosphoglucose isomerase

Enzymes.
 

Aspartate transaminase (EC 2.6.1.1)

 

catalase (EC 1.11.1.6)

 

3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35)

 

malate dehydrogenase (EC 1.1.1.37)

 

glucose-6-phosphate isomerase (EC 5.3.1.9)

 

succinate dehydrogenase (EC 1.3.99.1)

Ancillary