Inhibition of tyrosylprotein sulfotransferase by sphingosine and its reversal by acidic phospholipids.

Abstract

Although tyrosylprotein sulfation has been implicated in the processing of several secretory proteins, nothing is known about the regulation of the enzyme responsible for this event. When poly(Glu6, Ala3, Tyr1) (EAY; M(r) 47,000) was employed as sulfate acceptor, the tyrosylprotein sulfotransferase (TPST) from Golgi membranes of submandibular salivary gland was used to study the effect of various lipids on the expression of its activity. The TPST activity in the Golgi membrane was 38 pmol (mg of protein)-1 (30 min)-1. Approximately 90% of the total activity present in Golgi membranes was extracted by NaCl and Triton X-100 treatment. The Km values of solubilized TPST for EAY and 3'-phosphoadenosine 5'-phosphosulfate (PAPS) were 0.04 and 0.25 microM, respectively. Among the various lipids tested, sphingosine showed maximum inhibition of TPST activity followed by sphingomyelin and phosphatidylcholine (PC). Of the two sphingosine analogs tested, threosphinganine was as effective as sphingosine in TPST inhibition, while erythrosphinganine had little effect. In contrast, the acidic phospholipids phosphatidylinositol (PI) and phosphatidylserine (PS) and oleic acid showed slight stimulation. Half-maximal inhibition of TPST was obtained at 150 microM sphingosine (6 mol % when expressed as mole percent of sphingosine to total phospholipids plus Triton X-100). The inhibition was competitive with respect to EAY and uncompetitive with respect to PAPS. The inhibition caused by sphingosine could be reversed by PI, PS, and oleic acid but not by PC and sphingomyelin. Sphingosine inhibition of TPST activity was also observed in the enzyme isolated from several other tissues such as liver, lung, heart, and cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)