SULFATE ACTIVATION AND TRANSPORT IN MAMMALS - SYSTEM COMPONENTS AND MECHANISMS

Extensive studies on the mammalian sulfate-activating enzymes and PAPS translocase have enhanced our understanding of the overall pathway of sulfate activation and utilization. Isolation of the PAPS-synthesizin g activities from rat chondrosarcoma and preparation of stable non-hyd rolyzable analogs of APS and PAPS have facilitated the kinetic charact erization of mammalian ATP sulfurylase and APS kinase. These studies p rovided the basis for further experimental work showing that APS, the labile intermediate product, is channeled directly between the sulfury lase and kinase active sites. The defect in the brachymorphic mutant m ouse lies in this channeling mechanism, thus interfering with efficien t PAPS production. The rat chondrosarcoma ATP sulfurylase and APS kina se activities, in fact, reside in a single bifunctional cytoplasmic pr otein, which has now been cloned and expressed. The mechanism by which PAPS reaches its sites of utilization in the Golgi lumen has also bee n elucidated: The PAPS translocase is a 230-kDa integral Golgi membran e protein which functions as an antiport. (C) 1998 Elsevier Science In land Ltd. All rights reserved.