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Hansenula hennricii synthetisiert die Aminosaure Tyrosin uber den Pretyrosin-Weg. Prephensaure wird bei diesem Organismus durch eine spezifische Aminotransferase zu Pretyrosin und dieses durch eine NAD+-abhangige Dehydrogenase zu Tyrosin umgewandelt. Eine Prephenat-Dehydrogenase konnte nicht nachgewiesen werden. Eine Pretyrosin-Dehydratase, die in der Lage ist, Pretyrosin in Phenylalanin umzuwandeln, wurde ebenfalls nicht gefunden.

Die Anthranilat-Phosphoribosylpyrophosphat-Phosphoribosyl-Transferase (PR-Transferase) von Hansenula henricii 38-10-2 hat ein Molekulargewicht von 70000 Dalton und ist mit keinem anderen Enzym aggregiert. Sie katalysiert die Zwei-Substratreaktion nach dem sequentiellen Typ. Die Km-Werte betragen 4,6 μm fur Anthranilsaure und 0,88 mm fur Phosphoribosylpyrophosphat (PRPP). Das Enzym unterliegt einer Substrathemmung durch Anthranilsaure (Ki = 30 μm) und zeigt negative Kooperativitat der Bindungsstellen fur dieses Substrat (n = 0,6). Fur eine volle Aktivitat ist die Anwesenheit von Mg2+-Ionen notwendig (Km = 56 μm). Durch 3-Hydroxyanthranilsaure wird die PR-Transferase bezuglich Anthranilsaure kompetitiv gehemmt (Ki = 12 μm).

Gel filtration was employed to estimate the molecular weights and to determine possible physical aggregation of enzymes [5-dehydroquinate synthase (DHQ synthase), 5-dehydroquinase (DHQase, EC 4.2.1.10), shikimate: NADP oxidoreductase (EC 1.1.1.25), shikimate kinase (EC 2.7.1.71), 3-enolpyruvylshikimate 5-phosphate synthase (EPSP synthase)] in the shikimate pathway in eleven species of yeasts. The five enzymes were not aggregated in extracts of Hansenula henricii, H. fabianii, H. anomala, Candida utilis, Pichia guilliermondii, and Lodderomyces elongisporus. Two enzymes (DHQase and shikimate:NADP oxidoreductase) were not separable by this method and by ion exchange chromatography, and we conclude that they exist as an aggregate in these yeasts. Evidence is presented for an enzyme aggregate containing five activities, with a molecular weight of approximately 280,000 in Rhodosporidium spaerocarpum, Rh. toruloides, Rhodotorula rubra, Saccharomycopsis lipolytica, and Saccharomyces cerevisiae. Similarities between the enzymes in the shikimate pathway of plants, bacteria, and other fungi and those of investigated yeasts are discussed.

The general control of amino acid biosynthesis was investigated in Hansenula henricii. By limitation for single amino acids in wild type strain and mutants no derepression of enzymes was caused. In prototrophic revertants however, obtained from auxotrophic mutants (his, pdx) enzyme activities were 2 - 17 times higher than in the wild type. In these revertants enzymes of the biosynthetic pathways for tryptophan, phenylalanine, tyrosine, arginine, histidine, cysteine, methionine, asparagine, threonine, and isoleucine were derepressed. The amino acid pool pattern of the revertants if completely different from that in the wild type strain. A discussion of possible mechanisms of general control of amino acid biosynthesis in H. henricii is presented.