The
NAD- and
NADP-dependent
aldehyde dehydrogenase (ALDH) activities were evaluated in two rat
hepatoma cell lines, namely the well-differentiated MH1C1 line and the less differentiated HTC line. Each activity was determined in parallel in isolated rat hepatocytes, for comparison. The aliphatic
aldehyde acetaldehyde (ACA) and the aromatic
aldehyde benzaldehyde (BA) were used as substrates. With the first substrate the ALDH activities found in the crude cytoplasmic extracts were lower in
hepatoma cells than in normal hepatocytes, especially when measured with
NADP as
coenzyme (ACA/
NADP). Otherwise, with
benzaldehyde as substrate the
NAD-dependent
enzyme activity (BA/
NAD) was increased about 9-fold in HTC cells over hepatocytes and decreased in MH1C1 cells, while the
NADP-dependent (BA/
NADP) activity was increased 38- and 2.5-fold in HTC and MH1C1 cell lines, respectively. Studies on the subcellular distribution of these
enzyme activities showed that the activity measured with
acetaldehyde and
NAD (ACA/
NAD) was almost equally distributed between the cytosol and the subcellular particles in the three cell populations, but the ACA/
NADP activity was shifted towards the cytosolic compartment in
hepatomas, especially in HTC cells. The BA/
NAD and BA/
NADP ALDH activities found in the organelles of
hepatoma cells were markedly reduced in comparison with hepatocytes, in favour of the cytosol. The most striking difference between the normal and the transformed cells was the 94-fold increase over hepatocytes of the BA/
NADP activity, found in the cytosolic fractions of HTC cells. MH1C1 cells showed a less pronounced (7.5-fold) enhancement of this tumour-associated specific activity.(ABSTRACT TRUNCATED AT 250 WORDS)