[Isolation, purification and properties of acetolactate synthase from cultured Lactococcus lactis]. / Vydelenie, ochistka i izuchenie svoistv atsetolaktatsintazy iz kul'tury Lactococcus lactis.

Acetolactate synthase catalyzing the synthesis of alpha-acetolactate was isolated from lactic acid bacteria Lactococcus lactis subsp. lactis biovar. diacetylactis 4 and purified. Acetolactate synthase was shown to be an allosteric enzyme with low affinity for the substrate: the Km for pyruvate was 70 mM. The curve relating the dependence of enzyme activity on pyruvate concentration had a sigmoid shape. The enzyme activity persisted for 24 h in the presence of stabilizers, pyruvate, and thiamine pyrophosphate. Acetolactate synthase had the pH optimums of 5.8 and 6.5-7.0 in acetate and phosphate buffers, respectively. The temperature optimum for this enzyme was 38-40 degrees C at pH 6.5. The molecular weight of acetolactate synthase was 150 kDa. In Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate showed that the enzyme consisted of three identical subunits with a molecular weight of 55 kDa.

[Isolation and purification of acetolactate synthase and acetolactate decarboxylase from a Lactococcus lactis culture]. / Vydelenie i ochistka tsetolaktatsintazy i atsetolaktatdekaroksilazy iz kul'tury Lactococcus lactis.

Enzymes catalyzing the synthesis and subsequent transformation of alpha-acetolactate (AcL)--acetolactate synthase (AcLS) and acetolactate decarboxylase (AcLDC)--were isolated and partially purified from the cells of lactic acid bacteria Lactococcus lactis ssp. lactis biovar. diacetylactis strain 4. The preparation of AcLS, purified 560-fold, had a specific activity of 358,300 U/mg protein (9% yield). The preparation of AcLDC, purified 4828-fold, had a specific activity of 140 U/mg protein (4.8% yield). The enzymes exhibited optimum activity at pH 6.5 and 6.0, respectively (medium, phosphate buffer). The values of apparent Km, determined for AcLS and AcLDC with pyruvate and AcL, respectively, were equal to 70 mM and 20 mM. AcLS appeared as an allosteric enzyme with low affinity for the substrate and a sigmoid dependence of the activity on the substrate concentration. In the case of AcLDC, this dependence was hyperbolic, and the affinity of the enzyme for its substrate was high (Km = 20 mM). Leucine, valine, and isoleucine were shown to be activators of AcDLC.

[Regulation of fodder yeast Candida tropicalis glutamine synthetase activity by the end products of glutamine metabolism]. / Reguliatsiia aktivnosti glutaminsintetazy kormovykh drozhzhei Candida tropicalis konechnymi produktami obmena glutamina

Effect of different products of glutamine metabolism on the activity of glutamine synthetase in the presence of Mg2+, and Mn2+ and Co2+ as cofactors is studied. All the metabolites studied are found to inhibit the glutamine synthetase activity in the presence of any cation listed. The degree and the character of the inhibition by one or other metabolite depended in a considerable degree on the nature of the cation presented in the reaction mixture (Mg2+, Mn2+ or Co2+). The mechanism of the cumulative effect of retroinhibitors under the change of Mg2+ or Mn2+ in the reaction mixture was the same.