The muscle isozyme of lactate dehydrogenase is inhibited by lactate. Steady-state kinetic analysis yielded the following data, with lactate either absent or present at a fixed concentration.

(a) Pyruvate is the substrate whose concentration is varied in one plot, NADH in the other. Identify each. Use an arrow and the appropriate letter (b, c, d, or e) to identify each of the following. 

(b) Reciprocal of V_max for the uninhibited enzyme. 

(c) The line representing data obtained in the presence of lactate acting as a competitive inhibitor with respect to the variable substrate. 

(d) The line representing data obtained in the presence of lactate acting as a noncompetitive inhibitor with respect to the variable substrate. 

(e) Reciprocal of K_M in the presence of lactate acting as a competitive inhibitor. 

(f) If K_M for NADH is 2 × 10^-5 M, then which of the following is the most appropriate NADH concentration to use when determining K_M for pyruvate: 10^-7 M,10^-6 M, 10^-5 M, 10^-4 M, or 10^-3 M?

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