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The effect of Coriolis K mixing on the γ decay of one-quasiparticle isomeric states is examined in transfermium nuclei with neutron number N=153. We consider a core-plus-quasiparticle coupling in which the K mixing sharply increases if the isomeric quasiparticle state closely approaches the rotational state with the same angular momentum I, but built on another quasiparticle state which is either directly coupled to the isomeric (ΔK=1) or connected with it through the intermediate mixing quasiparticle orbitals (ΔK>1). This mechanism is likely to explain the 38-ns Kπ=7/2+ isomer in 251Cf which is quasidegenerated with an Iπ=7/2+ rotation state built on Kπ=1/2+. Our model explains the enhancement of its decay by three orders of magnitude compared to the Kπ=7/2+ isomer in 249Cm. We suggest that the same mechanism could be of general importance for the isomer decay properties in a wide range of heavy odd-mass nuclei.