# Substrate inhibition fitting by uncompetitive mode (S-v plot)
# For a single data
# Written by S. Fushinobu (2019.10.22)
# Thanks to Carly Huitema & Geoff P Horsman
# Edit the parameters below
Subinh.df <- read.csv("/Users/fushi/Documents/R/Subinh.csv")
Mtitle <- "Uncompetitive substrate inhibition plot"  # main title of the plot
Substname <- "Substrate"
Substunit <- " (mM)"
Vunit <- " (units/mg)"
Kminit <- 4               # initial values for fitting
Vmaxinit <- 10
Kiinit <- 10

plot(Subinh.df$conc,Subinh.df$rate,main=Mtitle,xlim=c(0,max(Subinh.df$conc)),ylim=c(0,max(Subinh.df$rate)),xlab=paste(Substname,Substunit),ylab=paste("v",Vunit))

Subinh.nls <- nls(rate ~ (Vmax * conc / (Km + (1+conc/Ki)*conc)), data=Subinh.df, start=list(Km=Kminit, Vmax=Vmaxinit,Ki=Kiinit))
Km <- unname(coef(Subinh.nls)["Km"])
Vmax <- unname(coef(Subinh.nls)["Vmax"])
Ki <- unname(coef(Subinh.nls)["Ki"])
curve(Vmax*x/(Km+(1+x/Ki)*x),0,max(Subinh.df$conc),add=TRUE, lty=2)

text(0,max(Subinh.df$rate)/20,paste("Km = ",signif(Km,digits=3),"±",signif(summary(Subinh.nls)$parameters[1,2],digits=3),Substunit,"; Vmax = ",signif(Vmax,digits=3),"±",signif(summary(Subinh.nls)$parameters[2,2],digits=3),Vunit,"\nKi = ",signif(Ki,digits=3),"±",signif(summary(Subinh.nls)$parameters[3,2],digits=3),Substunit),adj=0)

text(max(Subinh.df$conc),max(Subinh.df$rate)/6,expression(italic(v) == over(italic(V)[max] * "[S]", italic(K)[m] + (1+"[S]"/italic(K)[i])*"[S]")),adj=1)