(A) BINDING 0.2 normal normal #A FH 50 100 0 bound (g/g cell protein) LDL LDL internal (µg/g cell 0.1- 0.0 9 0.5 0.0 fal (B) INTERNALIZATION 0.2 0.0 0.4+000 normal FH (C) REGULATION 50 1000 50 100 FH 100 normal normal normal 50 1000 50 100 LDL (g/mL) LDL (ug/mL) Figure 13-19 LDL metabolism in normal cells and in cells from patients with severe familial hypercholesterolemia (Problem 13-100). (A) Surface binding of LDL Assays at 4°C allow binding but not internalization. (B) Internalization of LDL After binding at 4°C, the cells are warmed to 37°C. Binding and uptake of LDL can be followed by labeling LDL either with ferritin particles, which can be seen by electron microscopy, or with radioactive iodine, which can be measured in a gamma counter. (C) Regulation of cholesterol synthesis by LDL B. In Figure 13-19B, internalization of LDL by normal cells increases as the external LDL concentration is increased, reaching a plateau 5-fold higher than the amount of externally bound LDL. Why does LDL enter cells from patients FH or JD at such a slow rate? C. In Figure 13-19C, the regulation of cholesterol synthesis by LDL in normal cells is compared with that in cells from FH and JD. Why does increasing the external LDL concentration inhibit cholesterol synthesis in normal cells, but affect it only slightly
Enzyme kinetics
In biochemistry, enzymes are proteins that act as biological catalysts. Catalysis is the addition of a catalyst to a chemical reaction to speed up the pace of the reaction. Catalysis can be categorized as either homogeneous or heterogeneous, depending on whether the catalysts are distributed in the same phase as that of the reactants. Enzymes are an essential part of the cell because, without them, many organic processes would slow down and thus will affect the processes that are important for cell survival and sustenance.
Regulation of Enzymes
A substance that acts as a catalyst to regulate the reaction rate in the living organism's metabolic pathways without itself getting altered is an enzyme. Most of the biological reactions and metabolic pathways in the living systems are carried out by enzymes. They are specific for their works and work in particular conditions. It maintains the best possible rate of reaction in the most stable state. The enzymes have distinct properties as they can proceed with the reaction in any direction, their particular binding sites, pH specificity, temperature specificity required in very few amounts.
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