Two forms of striatal tyrosine hydroxylase from DEAE-cellulose chromatography

Abstract

Tyrosine hydroxylase (TH) in freshly prepared 45,000 g supernatant from rat striatum was fractionated by DEAE-cellulose chromatography. The elution was made with 2 vols. of buffer (50 mM Tris, pH 7.4; 2 mM dithiothreitol) followed by 4 vols. of a linear NaCl gradient (0–0.3 M) in the same buffer. TH activity was eluted in two distinct peaks: one at about 0.1 M salt (I), and the other at 0.2 M salt (II). The relationship between the two enzymes peaks was examined as follows. (I) Incubation of the supernatant in the presence of cAMP-dependent protein kinase. 1 mM ATP, 10 mM Mg 2+, and 0.1 mM cAMP resulted in the elimination of peak I, with a concomitant increase of peak II. This shift of TH peaks was prevented when the protein kinase was blocked by the addition of its inhibitory modulator. (2) Incubation of the supernatant with alkaline phosphatase, an enzyme known to dephosphorylate a variety of phosphoproteins, resulted in the elimination of peak II, with a concomitant increase of peak I. (3) Only freshly prepared supernatants showed two distinct TH peaks from DEAE-cellulose. From supernatants held at 0°C for 24 h, peak II was markedly reduced and peak I concomitantly increased. Since peak II appears to be readily convertible to peak I, no further fractionation was attempted. From the data obtained here, we believe that peaks I and II are respectively the nonphosphorylated and phosphorylated forms of TH. Furthermore, the endogenous distribution of the two TH forms in striatum was altered by the administration of haloperidol (2 mg/kg, i.p.), a neuroleptic drug known to activate the enzyme via a cAMP-dependent mechanism. At 90 min after the treatment, there was a marked increase of peak II, with a concomitant decrease of peak I. Thus, this procedure provides a simple means for estimating the degree of phosphorylation of TH in vivo in catecholaminergic neurons under various physiological and pharmacological conditions.