Reference: Biol. Bull. 165: 100-109. (August, 1983) IRON ACCUMULATION IN TUNICATE BLOOD CELLS. I. DISTRIBUTION AND OXIDATION STATE OF IRON IN THE BLOOD OF BOLTENIA OVIFERA, STYELA CLAVA, AND MOLGULA MANHATTENSIS MARIA I. AGUDELO 1 , KENNETH KUSTIN 1 *, GUY C. MCLEOD 2 , WILLIAM E. ROBINSON 2 , AND ROBERT T. WANG 3 1 Department oj Chemistry, Brandeis University, Walt ham, MA 02254; 2 Harold E. Edgerton Research Laboratory, New England Aquarium, Boston, MA 02110; 3 'Department of Chemistry, Salem State College, Salem, MA 01970 ABSTRACT The iron concentration, oxidation state, and distribution in blood plasma and blood cells of three iron containing tunicates were determined. Preliminary studies are reported on the possible role of plasma proteins in iron uptake. Iron(II) concentration in the millimolar range was found in the blood cell cy-toplasm of all three species; no iron(III) in solution was detected in blood cells. Over 70% of the total iron in the cells is associated with the membranes. Although the iron concentration in S. clava blood cells is substantially greater than that in B. ovifera cells, the iron to protein ratio by weight is similar in both species. SDS-electrophoresis of B. ovifera blood showed two protein subunits com-mon to both plasma and blood cells. These two subunits are most likely the major components of the high molecular weight protein found in the plasma. This protein was shown to bind iron(III) when iron(III) citrate was added to the plasma. INTRODUCTION Mechanisms of metal ion transport and accumulation in living cells are now being investigated by new techniques (Marx and Aisen, 1981; Anderson and Morel, 1982), and new tools such as extended x-ray absorption fine structure, EXAFS (Tullius et al, 1980). Of the essential metallic elements, iron presents one of the most difficult systems to study in terms of elementary steps at the organism/envi-ronment and cell/plasma barriers. Studies with bacteria (Emery, 1982) provide de-tailed information on elementary steps in uptake, although information on com-parable processes in animals still remain obscure. Studies with tunicates have the potential to clarify several steps in the accumulation process. Tunicates (class Ascidiacea) accumulate relatively high concentrations of selected metal ions in certain blood cells. Best known is the ability of members of the order Enterogona to accumulate vanadium (Millar, 1966; Swinehart et al, 1974). We have identified several elementary steps in the selective vanadium uptake mechanism and a model for this process has been constructed (Dingley et al., 198 1 ). We have recently extended our investigations to include iron accumulating Pleurogona (Agudelo et al., 1982; Agudelo et al., 1983). In this paper we begin our analysis of the iron accumulation mechanism by detailing the distribution, concentration, and oxidation Received 21 March 1983; accepted 25 May 1983. Abbreviations. TEMED, N,N,N',N'-Tetramethylethylenediamine; SDS, sodium dodecyl sulfate; Bis, N,N'-Methylene-bis-acrylamide. * Author to whom all correspondence should be sent. 100
IRON ACCUMULATION IN TUNICATE BLOOD CELLS. I. DISTRIBUTION AND OXIDATION STATE OF IRON IN THE BLOOD OF BOLTENIA OVIFERA, STYELA CLAVA, AND MOLGULA MANHATTENSIS
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