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b-Poly(l-malate) is supposed to function in the storage and transport of histones, DNA polymerases and other nuclear proteins in the giant syncytical cells (plasmodia) of myxomycetes. Here we report on the biosynthesis of [ 14 C]b-poly(l-malate) from injected l-[ 14 C]malate in the plasmodium of Physarum polycephalum. The effects of KCN, arsenate, adenosine 5 H -(a,b-methylene)triphosphate, adenosine 5 H -(b,g-methylene)triphosphate, guanosine 5 H -(b,g-methylene)triphosphate, desulfo coenzyme A and phenylarsinoxid on b-poly(l-malate) synthesis were studied after their coinjection with l-[ 14 C]malate. The synthesis was not affected by KCN or desulfo coenzyme A, but was blocked by arsenate and adenosine 5 H -(a,b-methylene)triphosphate. The plasmodium lysate catalysed an l-malate-dependent ATP-[ 32 P]pyrophosphate exchange, but was devoid of b-poly(l-malate) synthetic activity under all experimental conditions tested. The results suggested an extramitochondrial synthesis of b-poly(l-malate), involving the polymerization of b-l-malyl-AMP. It is assumed that the lack of synthesis in the lysate is caused by the inactivation of b-poly(l-malate) polymerase involving a cell injury kinase pathway. Because injected guanosine 5 H -(b,g-methylene)triphosphate blocks the synthesis, the injury signal is likely to be GTP dependent.Keywords: malyl-AMP-ligase; Physarum polycephalum; plasmodium; polymalate polymerase; polymalate synthetase.b-Poly(l-malate) (PMLA) is a polyanion with a molecular mass ranging from 5 kDa to several hundred kilodaltons and is produced by the syncytic cell form of myxomycetes ([1] and references therein). It consists of l-malyl units, which are linked by ester bonds between the b-carboxylates. The a-carboxylates are free and ionized at neutral pH. The polymer receives strong interest because of its chemical reactivity, biodegradability and availability from sustainable feedstocks [2]. As an unconventional biopolymer, it seems to have a unique physiological role, which is currently being uncovered for the plasmodium of Physarum polycephalum [3,4]. The plasmodium, which specifically produces PMLA, is a single multinuclear giant cell [1]. The nuclei divide synchronously by closed mitosis [5]. The biochemistry behind the plasmodial status is not understood, but PMLA appears to be involved.Evidence comes from the correlation of growth with PMLA synthesis, the integration of newly synthesized PMLA into nuclei [6], the high nuclear level of PMLA comparable with the levels of histones and DNA, the maintenance of a constant nuclear PMLA content, although production rates vary between wild-type and mutant strains and under different growth conditions [6], the higher order complexes of PMLA with DNA-polymerases, histones and other proteins in the nuclei [3,4,7]. It has been assumed that PMLA functions as a storage and carrier molecule to maintain an even distribution of histones, DNA polymerases and other nuclear proteins in the giant cell [4]. A plasmodium-specific protein, polymalatase, has been identified...

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