A dual cofactor-specific isocitrate dehydrogenase fromPythium ultimum

Isocitrate dehydrogenase is considered to be one of the key regulatory enzymes in the conversion of glucose into fatty acids by oleaginous microorganisms. A dual coenzyme-specific isocitrate dehydrogenase (EC 1.1.1.41) (IDH) was isolated from the primitive fungus Pythium ultimum and purified by 211-fold by sequential ion-exchange, affinity, and gel filtration chromatographies. Specific activity of the partially purified enzyme was 76.2 μmol/(min∙mg protein) with NAD+and 40% less active with NADP+. Optimum pH for activity was 8.5–9.5. Kmvalues for threo-D-isocitrate and NAD+were 0.031 and 0.55 mM, respectively. The estimated molecular mass of the IDH was 96 kDa under nondenaturing conditions and 48 kDa under denaturing conditions, suggesting that the enzyme is composed of two subunits of the same size. The enzyme was relatively stable up to 55 °C, but no activity was detected after exposure to 65 °C for 15 min. Mg2+or Mn2+were required for activity.Key words: isocitric dehydrogenase, Pythium ultimum, dual cofactor specific, oleaginicity.

Evaluation of Heat Treatment of Turkey Breast Meat by Biochemical Methods

A biochemical method for the verification of heat treatment of turkey breast meat was developed. The activities of 12 enzymes and residual soluble proteins were studied following heat treatment at various temperatures for different durations. The enzymes aspartate aminotransferase, creatine kinase, malic dehydrogenase, lactic dehydrogenase, isocitric dehydrogenase, and aldolase, showing initial preheating high specific activities, were shown to be valuable markers for the evaluation of heat treatment. Other enzymes, showing low specific activities were of little diagnostic value. Enzyme activities decreased in response to the maximum temperature levels and duration in which the meat was treated. The activities of the enzymes creatine kinase, malic dehydrogenase, lactic dehydrogenase, and isocitric dehydrogenase as well as the residual soluble proteins were shown to be good markers for the evaluation of heat treatment of fresh meat. Soluble residual proteins could also be estimated with commercial test strips. The use of hemoglobin-myoglobin oxidative activity was tried and shown to be a potential test using existing commercial test strips.

THE TOLERANCE OF MANGO TO INSECTICIDAL OXYGEN ATMOSPHERE

Mango fruits (cv Keitt) were exposed to a continuous flow of low O2 atmosphere of 0.1 to 0.2% (balance is N2) for 0 to 5 days at 20°C. Fruits were evaluated every day after exposure to low O2 atmosphere, and again after 5 days in air at 20°C. A sensory evaluation test was conducted after 15 days from the initiation of the experiment. The low O2 atmosphere reduced the activity of the enzymes malic dehydrogenase and isocitric dehydrogenase but did not affect the activity of α- Ketoglutarate dehydrogenase. However, there was no indication of any fruit injury nor any detrimental organoleptic changes due to the low O2 atmosphere. These results suggest the possibility of the application of very low O2 atmosphere for postharvest insect control in mango.