The aim of this study is to characterize the function of mitochondria and main energy fluxes in human
colorectal cancer (HCC) cells. We have performed quantitative analysis of cellular respiration in post-operative tissue samples collected from 42
cancer patients. Permeabilized
tumor tissue in combination with high resolution respirometry was used. Our results indicate that HCC is not a pure glycolytic
tumor and the oxidative phosphorylation (OXPHOS) system may be the main provider of
ATP in these
tumor cells. The apparent Michaelis-Menten constant (Km) for
ADP and maximal respiratory rate (Vm) values were calculated for the characterization of the affinity of mitochondria for exogenous
ADP: normal colon tissue displayed low affinity (Km = 260 ± 55 μM) whereas the affinity of
tumor mitochondria was significantly higher (Km = 126 ± 17 μM). But concurrently the Vm value of the
tumor samples was 60-80% higher than that in control tissue. The reason for this change is related to the increased number of mitochondria. Our data suggest that in both HCC and normal intestinal cells
tubulin β-II
isoform probably does not play a role in the regulation of permeability of the MOM for
adenine nucleotides. The
mitochondrial creatine kinase energy transfer system is not functional in HCC and our experiments showed that
adenylate kinase reactions could play an important role in the maintenance of energy homeostasis in
colorectal carcinomas instead of
creatine kinase. Immunofluorescent studies showed that
hexokinase 2 (HK-2) was associated with mitochondria in HCC cells, but during
carcinogenesis the total activity of HK did not change. Furthermore, only minor alterations in the expression of HK-1 and HK-2
isoforms have been observed. Metabolic Control analysis showed that the distribution of the control over electron transport chain and
ATP synthasome complexes seemed to be similar in both
tumor and control tissues. High flux control coefficients point to the possibility that the mitochondrial respiratory chain is reorganized in some way or assembled into large supercomplexes in both tissues.