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 isoen zymes in the sera of patients with liver tumours, using class-specific fluo rogenic naphthaldehydes as substrates. The activity of the tested isoenzyme s 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 isoenzyme s in secondary tumours seems to be caused by the enzyme released from prima ry cells originating in the other organs, but increased total enzyme activi ty measured with chromogenic substrates may be proof of the presence of oth er classes of isoenzymes. These results show that the elevated class I isoe nzymes and total enzyme activity in the sera of patients with liver tumours may indicate the metastatic origin of these tumours.