Curve fitting in R

MM <- function(reads, Gm, K){    
	(Gm * reads)/(K + reads)
}

model <- nls( y ~ MM(x, Gm, K), data = data.frame(x,y), start = list(Gm = 4000, K = 10))
coef(summary(model))

xlim = c(min(x),max(x))
plot(x,y,xlim=xlim)

line.x = seq(xlim[1],xlim[2],length=100)
line.y = predict(model, newdata=list(x=line.x))
lines(line.x,line.y,col='red',lty='dotted')