Which of the following is/are true regarding initial and maximal velocity of enzyme-mediated reactions?

a. At very low substrate concentrations, the initial velocity of an enzyme reaction will be lower than the maximal velocity of the enzyme reaction.
b. When an enzyme behaves with Michaelis-Menten kinetics, the initial velocity of that enzyme reaction changes with substrate concentration, but the maximal velocity of that particular enzyme remains the same at a constant enzyme concentration and identical reaction conditions
c. Initial velocity is maintained until maximal velocity is reached.
d. The initial velocity is determined by the slope of the line at the beginning of a reaction when one plots the experimental results of reaction time versus product formed. Maximal velocity is then determined by when the initial velocity no longer significantly changes with increasing substrate concentration.

Here since the [tex]$V_0$[/tex] varies directly to the substrate concentration [S], the initial velocity is lower than the maximal velocity. Thus option (a) is true.

b). The Michaelis -Menten kinetics equation states that :

[tex]$V_0 = \frac{V_{max} \times [S]}{Km+[S]}$[/tex]

Here the initial velocity changes directly with the substrate concentration as [tex]$V_0$[/tex] is directly proportional to [S]. But [tex]$V_{max}$[/tex] is same for any particular concentration of the enzymes. Thus, option (b) is true.

c). As the substrate concentration increases, the initial velocity also increases. Thus option (c) is false.

d). Option (d) explains the procedures to estimate the initial velocity which is correct. Thus, option (d) is true.