Reversible and Irreversible Inhibition of Hypo-Xanthine-Phosphoribosyltransferase

Abstract

For some years our laboratory has been concerned with the purification and characterization of hypoxanthine-phosphoribosyltransferase (HPRT, EC 2.4.2.8) from rat brain. By a new method (which will be discussed in detail in the methodologysection of this meeting) we now can easily obtain pure HPRT from rat brain or human erythrocytes and use these enzyme preparations to produce antisera in rabbits. It has been reported by several authors, also in this symposium 3 years ago, that specific antisera do inhibit HPRT-activity and we cannot add any exciting new evidence to this point. So only the antirat and anti-human serum shall shortly be compared with one another:

• Both sera inhibit their respective enzymes.

• Best results are obtained when the serum after having reacted with the enzyme is precipitated by goat-anti-rabbit-IgG.

• Anti-rat-serum does not crossreact with human HPRT.

• Anti-human-serum does not crossreact with rat HPRT.

• As expected both sera do not crossreact with rabbit HPRT (for example with the enzyme of the animal that produced the antiserum).

• Especially in the human system we found when — after reaction of the antiserum with the enzyme — samples are not carefully centrifuged, or are not precipitated with goat-antirabbit- IgG, or when an excess of antiserum was used, soluble enzyme-antibody-complexes are formed which are still enzymatically active.