Histamine exerts each of the following effects EXCEPT: A. Dilation of small blood vessels, leading to a flushing of the skin B. Increased capillary permeability, leading to edema C. Bronchoconstriction, leading to difficult breathing D. Reduced secretion of gastric acid, leading to protection of the gastric mucosa

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enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products