The activity of class I and II alcohol dehydrogenase isoenzymes in the sera of patients with liver tumours.

We have measured the activity of class I and II alcohol dehydrogenase isoenzymes in the sera of patients with liver tumours, using class-specific fluorogenic naphthaldehydes as substrates. The activity of the tested isoenzymes was unchanged in primary tumours and significantly increased (class I) in metastatic liver tumours. The total enzyme activity was also increased (3-fold) in this group of patients. The elevated activity of class I isoenzymes in secondary tumours seems to be caused by the enzyme released from primary cells originating in the other organs, but increased total enzyme activity measured with chromogenic substrates may be proof of the presence of other classes of isoenzymes. These results show that the elevated class I isoenzymes and total enzyme activity in the sera of patients with liver tumours may indicate the metastatic origin of these tumours.