PREFERENTIAL DECARBOXYLATION OF HYDROPHILIC PHOSPHATIDYLSERINE SPECIES IN CULTURED-CELLS - IMPLICATIONS OF THE MECHANISM OF TRANSPORT TO MITOCHONDRIA AND CELLULAR AMINOPHOSPHOLIPID SPECIES COMPOSITIONS

Citation
L. Heikinheimo et P. Somerharju, PREFERENTIAL DECARBOXYLATION OF HYDROPHILIC PHOSPHATIDYLSERINE SPECIES IN CULTURED-CELLS - IMPLICATIONS OF THE MECHANISM OF TRANSPORT TO MITOCHONDRIA AND CELLULAR AMINOPHOSPHOLIPID SPECIES COMPOSITIONS, The Journal of biological chemistry, 273(6), 1998, pp. 3327-3335
Citations number
65
Categorie Soggetti
Biology
ISSN journal
00219258
Volume
273
Issue
6
Year of publication
1998
Pages
3327 - 3335
Database
ISI
SICI code
0021-9258(1998)273:6<3327:PDOHPS>2.0.ZU;2-0
Abstract
In baby hamster kidney and other cultured cells the majority of phosph atidylethanolamine (PE) is synthesized from phosphatidylserine (PS) in a process which involves transport of PS from the endoplasmic reticul um to mitochondria and decarboxylation therein by PS decarboxylase. To study the mechanism of this transport process, we first determined th e molecular species composition of PE and PS from baby hamster kidney and Chinese hamster ovary cells. Interestingly, the hydrophilic diacyl molecular species were found to be much more abundant in PE than in P S, suggesting that hydrophilic PS species may be more readily transpor ted to mitochondria than the hydrophobic ones. To study this, me compa red the rates of decarboxylation of different PS molecular species in these cells. The cells were pulse labeled with [H-3]serine whereafter the distribution of the labels among PS and PE molecular species was d etermined by reverse phase high performance liquid chromatography and liquid scintillation counting. The hydrophilic PE species contained re latively much more H-3 label than those of PS, which indicates that th ey are more readily decarboxylated than the hydrophobic ones. Control experiments showed that differences in [H-3]PS and -PE molecular speci es profiles are not due to (i) incorporation of H-3 label to some PE s pecies via alternative pathways, (ii) differences in degradation or re modeling among species, or (iii) selective decarboxylation of PS molec ular species by the enzyme. Therefore, hydrophilic PS species are inde ed decarboxylated faster than the hydrophobic ones. The rate of decarb oxylation decreased systematically with hydrophobicity, strongly sugge sting that formation of so called activated monomers, i.e. lipid molec ules perpendicularly displaced from the membrane (Jones, J. D., and Th ompson, T. E. (1990) Biochemistry 29, 1593-1600), is the rate-limiting step in the transport of PS from the endoplasmic reticulum to mitocho ndria. The formation of activated monomers and thus the rate of transf er is probably greatly enhanced by frequent collisions between the two membranes which tend to be closely associated. The present data also provides a feasible explanation why hydrophilic molecular species in t hese cells are much more abundant in PE as compared with PS, its immed iate precursor.