S -6 3Enz y meschapter61. Keeping the Sweet Taste of Corn The sweet taste of freshly picked corn (maize) is due to the high level of sugar in the kernels. Store-bought corn (several days after picking) is not as sweet,because about 50% of the free sugar is converted to starch within one day of picking. To preserve thesweetness of fresh corn, the husked ears can be immersed in boiling water for a few minutes(“blanched”) then cooled in cold water. Corn processed in this way and stored in a freezer maintainsits sweetness. What is the biochemical basis for this procedure?Answer After an ear of corn has been removed from the plant, the enzyme-catalyzed conver-sion of sugar to starch continues. Inactivation of these enzymes slows down the conversion toan imperceptible rate. One of the simplest techniques for inactivating enzymes is heat denatura-tion. Freezing the corn lowers any remaining enzyme activity to an insignificant level.2. Intracellular Concentration of EnzymesTo approximate the actual concentration of enzymes in abacterial cell, assume that the cell contains equal concentrations of 1,000 different enzymes in solutionin the cytosol and that each protein has a molecular weight of 100,000. Assume also that the bacterialcell is a cylinder (diameter 1.0 mm, height 2.0 mm), that the cytosol (specific gravity 1.20) is 20% solu-ble protein by weight, and that the soluble protein consists entirely of enzymes. Calculate the averagemolar concentration of each enzyme in this hypothetical cell.Answer There are three different ways to approach this problem.(i)The concentration of total protein in the cytosol isϭ 0.24 ϫ 10Ϫ5 mol/mL ϭ 2.4 ϫ 10Ϫ3 MThus, for 1 enzyme in 1,000, the enzyme concentration ...
