Lipoamidase activity in virus induced tumours and in the corresponding normal tissue.

Abstract

Increased glycolysis in tumour tissue has first been observed by W A R B U R G in 1 9 2 3 and has since been postulated to be the origin of tumour formation 1. One possibility to increase the production of lactate, is to prevent the conversion of pyruvate, which is derived from glucose via the E m d e n M e y e r h o f pathway, into acetyl-CoA. Pyruvate will then function as a hydrogen acceptor from NADH, resulting in the formation of lactic acid. The conversion of pyruvate into acetyl-CoA is catalysed by the pyruvate dehydrogenase complex which contains covalently bound lipoic acid as cofactor 2 . This cofactor can be released by lipoamidase3 causing inactivity of the pyruvate dehydrogenase complex. Since virally induced tumours also have an increased glycolytic activity 4 , it was investigated whether tumour viruses can induce lipoamidase activity. 35S-proteins from E. coli including lipoic acid were, therefore, incubated with homogenates of yeast, known to contain lipoamidase5 . They served as a control. In addition, extracts of SV 40 — and RSV — induced tumours and homogenates of hamster kidney and chicken muscle (corresponding normal tissues) were tested. The released radioactive lipoic acid was extracted with benzene and identified by thinlayer chromatography. The radiochromatogram (see Fig. 1) shows the results obtained with the tumour induced by the DNA containing SV 40 virus. It can be seen that lipoamidase activity is present in yeast but neither in the tumour nor in the kidney tissue. The same result was obtained when a tumour induced by the R N A virus RSV was compared with chicken muscle. In both cases lipoamidase activity was absent. An increased glycolysis in virus induced tumours via an induction of lipoamidase can therefore be excluded.