СВЕРХСИНТЕЗ α-АЦЕТОЛАКТАТА ИЗ ГЛЮКОЗЫ У ПРОДУЦЕНТА ДИАЦЕТИЛА LACTOCOCCUS LACTIS SSP. LACTIS BV. DIACETYLACTIS В2103, ПРИРОДНОГО МУТАНТА, ЛИШЕННОГО α-АЦЕТОЛАКТАТДЕКАРБОКСИ-ЛАЗЫ

Abstract

The effect of oxygen supply rate on the activity of pyruvate metabolic pathways and their end products (lactate-dehydrogenase (LDH), pyruvate-formate-lyase (PFL), pyruvate-dehydrogenase (PDH) and acetolactate-synthase (ALS) pathways) in Lactococcus lactis ssp. lactis bv. diacetylactis B2103/74 strain has been investigated. In was found out that this culture, apart from inactivated а-acetolactate decarboxylase, possesses a unique natural capacity of oversynthesizing а-acetolactate (AL) up to 25—28 mM. The search for analogous strains in the diacetilicus bv. showed that this evidence is relatively infrequent; only one culture (VKPM 7590) was shown to have the same capacity. However, unlike the B2103/74 strain, the 7590 culture has an active а-acetolactate decarboxylase, and therefore, it is only able to produce acetoin. The oversynthesis of AL was observed at intense aeration (K L a > 90—120 h -1 ); medium composition played a decisive role in the process. It was shown that a powerful shift of a part of the pyruvate flow from the LDH- to PDH- and ALS-pathway underlies the evidence of LA oversynthesis, and due a restricted throughout capacity of the PDH-pathway, all the metabolism of the additional pyruvate supplied from the LDH-pathway proceeded exclusively through the ALS- avoiding the PDH-pathway. The shift of the pyruvate metabolism from the LDH- to PDH- and ALS-pathways in the B2103/74 culture is associated with the initiation of the oxidase reaction that reduces oxygen to H 2 O and therefore overshoots for this purpose NADH from LDH. The specific manifestation of this reaction in the B2103/74 and 7590 cultures that resulted in a deep rearrangement of all pyruvate metabolism for the production of а-acetolactate is owing to the occurrence of a superactive oxidase system that shifts 75—80% of the NADH flow from LDH to the oxidase pathway for NAD + regeneration. The origin of this superoxidase system is unknown. It is suggested that it can be close in structure to a simplest membrane-built electron-transport chain.