| | Re: DNA Polymerase for PCR (pfx-invitrogen)
I haven't used Pfx Invitrogen, but I've used Pfu polymerase from other brands. My general opinion is that for Pfu, it's much trickier than regular Taq. The brands I've used suggest varying amounts, and I find that it's generally between 1.25 - 2.5 U (depending on the enzyme concentration).
I'm not entirely sure bout the 1 unit recommended for Pfx. That is actually lower than the amount recommended for Pfu by other brands. For GeneRacer (Invitrogen), the recommended amount of Pfx is 1.25 U (0.5 ul in 50 ul reaction), whereby it is for a type of difficult PCR.
You could try using 1 U, but I would suggest increasing it slightly to 1.25 U if you're not getting any reactions. Plus if you're adding any additives (eg. DMSO, betaine, etc), you definitely need a higher amount as these additives partially inhibit Pfu activity.
In general, for myself I use 1.25 U of Pfu for a no-frills PCR, and 2.5 U of Pfu when I'm adding in additives or I believe it's a difficult template.
p/s: I hope you're not doing 50ul PCR reactions. Pfu isn't cheap, and I usually run 15 ul reactions if it's a new PCR or I'm not certain of the results.