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We study the impact of recent measurements of charm cross section H1-ZEUScombined data on simultaneous determination of parton distribution functions(PDFs) and the strong coupling, $\alpha_s(M^2_Z)$, in two different schemes. Weperform several fits based on Thorne-Roberts (RT) and Thorne-Roberts optimal(RTOPT) schemes at next-to-leading order (NLO). We show that adding charm crosssection H1-ZEUS combined data reduces the uncertainty of the gluon distributionand improves the fit quality up to $\sim 0.4$~\% and $\sim 0.9$~\%~, withoutand with the charm contribution, from the RT scheme to the RTOPT scheme,respectively. We also emphasise the central role of the strong coupling,$\alpha_s(M^2_Z)$, in revealing the impact of charm flavour contribution, whenit is considered as an extra free parameter. We show that in going from the RTscheme to the RT OPT scheme, we get $\sim 0.9$~\% and $\sim 2.0$~\%~improvementin the value of $\alpha_s(M^2_Z)$, without and with the charm flavourcontribution respectively.

Impact of Charm H1-ZEUS Combined data and Determination of the Strong Coupling in Two Different Schemes