Transition of hemoglobin between two tertiary conformations: determination of equilibrium and thermodynamic parameters from the reaction of 5,5'-dithiobis(2-nitrobenzoate) with the CysF9[93]beta sulfhydryl group

The equilibrium constant of the reaction of 5,5'-dithiobis(2-nitrobenzoate) with the CysF9[93]beta sulfhydryl group of hemoglobin decreases by 2 to 3 orders of magnitude between pH 5.6 and 9. The reaction is coupled to the ionizations of two groups on the protein. At 25 degrees C one group has a pK(a) of 5.31+/-0.2 when hemoglobin is in its (tertiary) r conformation, typified by the thiolate anion form of CysF9[93]beta; this changes to 7.73+/-0.4 in the (tertiary) t conformation, typified by the mixed disulfide form of the sulfhydryl. The second group ionizes with a pK(a) of 7.11+/-0.4 in the r conformation; this changes to 8.38+/-0.2 in the t conformation. K(rt), the equilibrium constant for the r<-->t isomerization process, is 0.22+/-0.06. The standard enthalpy and entropy changes for the isomerization are DeltaH(o)(rt)=24.2 kJ mol(-1) and DeltaS(o)(rt)=68.8 JK(-1)mol(-1), respectively.     

Carriers for starter cultures for the production of garri,a fermented food derived from cassava

Garri is a popular food in Nigeria derived from the fermentation of the mash obtained from the enlarged root of the cassava plant, Manihot esculenta Crantz. As currently produced, the mash used for garri production is spontaneously fermented; on account of this, there is great variability in the organoleptic properties and the quantities of residual cyanide in the garri from Nigeria. The use of starter cultures can help ensure uniformity in these properties if dry carriers can be found on which the fermentative organisms can survive for extended periods so as to facilitate the transportation of their carriers to the many small and scattered garri producers. We therefore studied the survival, singly or mixed, on dry starchy substrates derived from locally available crops, of Lactobacillus coryneformis, Lact. delbruckii, and Saccharomyces sp., which are associated with garri production, as carriers for these organisms. After 16 weeks of storage, between 75% and 85% of the organisms survived on yam, coco-yam, cassava in that order, whereas between 40 and 65% survived on rice and garri. Refrigeration at 4 °C did not improve the survival of the organisms, when compared to room temperature (30 °C) for the organisms stores on yam, coco-yam, and cassava. However where the organisms were stored on rice and garri, refrigeration improved the survivability of the organisms by between 10 and 20%.