Compartmentation and Activities of Enzymes Involved in the Metabolism of Amino Acids Implicated in Osmoregulatory Mechanisms in Acanthamoeba castellanii1

Glutamate dehydrogenase in Acanthamoeba castellanii is an NAD-dependent cytosolic enzyme. This is similar to glutamate dehydrogenases in Phycomycetes, but very different from the dual coenzyme-specific enzymes located in mitochondria in animals and in mitochondria and chloroplasts in higher plants. Pyrroline-5-carboxylate (P-5-C) reductase occurs also in the cytoplasm in A. castellanii and has very high affinities for L-P-5-C (K_m= 12 μM) and NADH (K_m= 15 _μM). In contrast, ornithine aminotransferase and proline oxidase are mitochondrial enzymes. No proline-inhibited γ-glutamyl kinase was detected while an active glutamine synthetase was found in the cytosolic compartment. Evidence for a mitochondrial transport system for L-proline was obtained. Two possible pathways for proline biosynthesis in A. castellanii are discussed based on information obtained about activities and subcellular compartmentation of enzymes.     

Functional morphology and evolution of the cystoid Echinosphaerites

Echinosphaerites , known from the Lower and Middle Ordovician, has branched biserial brachioles. Such features are so far unknown in the Rhombifera. Echinosphaerites had a skeletal meshwork like that of other blastozoan echinoderms, with a fine outer mesh layer and an inner coarse mesh layer. During evolution the number and location of brachioles, including the pattern of brachiole branching, changed by increase in the number of brachioles and increased complexity of the branching pattern. The exothecal pore structures increased in the complexity of patterns of tangential canals. The pattern of skeletal growth in Echinosphaerites is discussed. The Echinosphaeritidae and Caryocystitidae families are closely related and show parallel development.     

The name Cryptolepis bifida L.Joubert & Venter,a later homonym of C. bifida (Blume) P.I.Forst., corrected

A new Cryptolepis species from Kenya and Tanzania was named Cryptolepis bifida L.Joubert & Venter. However, this name is a later homonym of Cryptolepis bifida (Blume) P.I.Forst. and is herewith corrected to Cryptolepis ibayana L.Joubert & Venter. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 355.