methionine sulfoxide reductase b1 deficiency does not increase highfat dietinduced insulin resistance in mice methioninessulfoxide reductase msra protects against highfat dietinduced insulin resistance due to its antioxidant effects to determine whether its counterpart methioninersulfoxide reductase msrb has similar effects we compared msrb1 knockout and wildtype mice using a hyperinsulinemiceuglycemic clamp technique highfat feeding for eight weeks increased body weights fat masses and plasma levels of glucose insulin and triglycerides to similar extents in wildtype and msrb1 knockout mice intraperitoneal glucose tolerance test showed no difference in blood glucose levels between the two genotypes after eight weeks on the highfat diet the hyperglycemiceuglycemic clamp study showed that glucose infusion rates and whole body glucose uptakes were decreased to similar extents by the highfat diet in both wildtype and msrb1 knockout mice hepatic glucose production and glucose uptake of skeletal muscle were unaffected by msrb1 deficiency the highfat dietinduced oxidative stress in skeletal muscle and liver was not aggravated in msrb1deficient mice interestingly whereas msrb1 deficiency reduced jnk protein levels to a great extent in skeletal muscle and liver it markedly elevated phosphorylation of jnk suggesting the involvement of msrb1 in jnk protein activation however this jnk phosphorylation based on a pjnkjnk level did not positively correlate with insulin resistance in msrb1deficient mice taken together our results show that in contrast to msra deficiency msrb1 deficiency does not increase highfat dietinduced insulin resistance in mice