Specificity and Direction of Depolymerization of β‐Poly(L‐malate) Catalysed by Polymalatase from Physarum polycephalum

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Abstract
β‐Poly(l‐malate), a major constituent of nuclei in plasmodia of Physarum polycephalum, is enzymatically degraded to l‐malate after secretion into the culture medium. This depolymerization is specifically catalysed by an endogenous polymalatase. The mode of action and the specificity criteria have been investigated by employing various chemical derivatives of β‐poly(l‐malate), including substitution at the hydroxy‐terminus and carboxy‐terminus of the polymer, esterification of the pending α‐carboxylate, and β‐poly(dl‐malate). The results of the investigation were summarized in a specificity model that involved recognition of the hydroxy‐terminus and of the α‐carboxylate as substituents of the asymmetric carbon in the malic acid unit. Depolymerization proceeded from the hydroxy‐terminus towards the carboxy‐terminus, thereby degrading the polymer to l‐malate. When the terminal β‐carboxylate had been amidated with the fluorescent N‐(1‐naphthyl)ethylenediamine, degradation was normal but was arrested at the level of the terminal β‐carboxy‐substituted dimer. It should be possible to employ polymalatase as a tool for the detection of branching and other modifications of β‐poly(l‐malate).

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