Subcellular Distribution of a Factor Inactivating Tyrosine Aminotransferase

Abstract

The subcellular distribution of ii tyrosine aminotransferase inactivating factor in rat liver has been investigated. Most of its activity is associated with plasma membranes, with minor amounts in mitochond ria and endo plasma tic ret icul um.The factor is also found in kidney and inactivates the enzyme reversibly in presence of cysteine, most likely by modification of -SH groups.ATP counteracts this inactivation only, when crude enzyme extracts are inactivated by purified subcellular fractions or when the purified enzyme is inactivated in presence of liver or kidney cortex homogenates.The relationship of this inactivation to reported different forms of the enzyme has been investigated. Form I of three different forms, that can be obtained by hydroxyl-apatite chromatography, is readily inactivated, form I11 can be partly converted to form I by incubation in presence of purified plasma membranes.The relationship of these findings to a possible multistep mechanism in the turnover of the enzyme is discussed.

Tyrosine aminotransferase: biochemical and structural properties and molecular dynamics simulations

“…The formation of an intra or inter TAT disulphide bond was long ago proposed as being involved in the inactivation of the enzyme (Beneking et al, 1978; Buckley and Milligan, 1978; Federici et al, 1978). An important feature of the observed inactivation was its reversibility by thiol compounds (Beneking et al, 1978; Federici et al, 1978). Our findings of a disulphide bond formation between Cys144 and Cys275 residues support this previous suggestion.…”

Participation of cysteine and cystine in inactivation of tyrosine aminotransferase in rat liver homogenates

“…While the present work was being prepared for publication, Beneking et al (1978) reported that a factor associated mainly with plasma membranes inactivated purified tyrosine aminotransferase in the presence of cysteine. The rate of inactivation varied between different forms of the enzyme, and it was suggested (Beneking et al, 1978) that the variation was due to the time required for conversion to the most readily inactivated form.…”

“…The rate of inactivation varied between different forms of the enzyme, and it was suggested (Beneking et al, 1978) that the variation was due to the time required for conversion to the most readily inactivated form. The existence of multiple forms of tyrosine aminotransferase has been demonstrated by several laboratories, and Rodriguez & Pitot (1976) have found that the multiple forms possess different numbers of thiol groups.…”

How many distinct enzymes are responsible for the several cellular processes involving thiol:protein‐disulphide interchange?

“…Brocklehurst and Kierstan [44] propose that propapain, a catalytically-inactive protein found in Tyrosine aminotransferase from rat liver exists in 3 separable forms, which may be relevant to the in vivo regulation of the enzyme. The forms are interconvertible in vitro, and the nature of the differences between them, and of factors which catalyse their interconversion, have been studied intensively [45][46][47]. At present the evidence suggests that the forms differ in free thiol content and that the cellular systems catalysing their interconversion are catalysts of thiol:disulphide interchange [45].…”