Lineweaver-Burk replots for enzyme inhibition prints regression lines intersecting themselves on quadrant I. The interpretations for competitive, noncompetitive, or uncompetitive inhibition does not fit well the data. Data looks like a competitive inhibition shifted to the right, away from the y-axis. Is there the possibility of the existence of a mixed-type inhibition which explains our data?
If you are looking at a monosubstrate reaction, there is one case in which linear Lineweaver-Burk plots intersect in quadrant 1. This is one of the 6 cases of nonlinear hyperbolic inhibition, case 6: hyperbolic noncompetitive inhibition.
Reference: V. Leskovac, Comprehensive Enzyme Kinetics, 2003 page 99.
"The inhibitor not only decreases the rate constant for product formation, but also markedly increases the affinity of the enzyme for the substrate. For example, at a fixed inhibitor concentration, the inhibitor acts as an activator below a certain fixed concentration of substrate and as an inhibitor above that concentration. Thus, in this case, there may be some doubt whether to call I an inhibitor or an activator."
There is more detail in the book, including equations.
However, before concluding that you are seeing this exotic mechanism, you should make sure that what appears to be crossing in quadrant 1 is not just an artifact of scatter in the data, or some experimental artifact.
I agree with Adam B Shapiro: Find out if your values really are unusual, and only then think about what they might mean. You could forego linearisation and use the "direct plot" of Cornish-Bowden and Eisenthal (DOI:10.1042/bj1390721, DOI:10.1042/bj1390715). This results in robust and unbiased estimates of Km and Vmax, together with error range. This method is of particular importance if the velocity measurements have scatter. I have given a worked-out example for the use of this plot in DOI:10.1007/978-3-319-19920-7_6, which may be helpful.
I agree with Prof. Adam B Shapiro, this article will help you ( V. Leskovac, Comprehensive Enzyme Kinetics, 2003 page 99. )
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