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Lack of muscle glycogen phosphorylase activity leads to McArdle's disease, a rare metabolic myopathy. To investigate its molecular basis at the nucleic acid level, we isolated muscle phosphorylase cDNA clones from a human cDNA library in Escherichia coli plasmid pBR 322. Subcloning of one insertion of M13 bacteriophage permitted its definite identification by sequencing. Northern blot experiments revealed one specific messenger RNA of 3.4 kilobases found uniquely in tissues expressing muscle phosphorylase.We show that McArdle's disease exhibits a molecular heterogeneity at the messenger RNA level. In eight unrelated cases of McArdle's disease in which no inactive proteins had been detected, we assayed muscle biopsies for phosphorylase mRNA by Northern blotting. In five cases, no muscle phosphorylase mRNA could be detected, while in three other cases, normal length mRNA was present in lower amounts.Moreover, Southern blot analysis of DNA isolated from white blood cells in four McArdle patients revealed no major deletion or rearrangements of the phosphorylase gene as compared with controls.

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An isolation procedure for rat brain aldolase C has been developed which also permits the isolation of aldolase C from experimental hepatomas.Certain enzymatic properties (specific activity and Michaelis constant towards the two specific substrates : fructose 1,6-bisphosphate and fructose 1 -phosphate) and physico-chemical properties (molecular weight, N-terminal amino-acid) of the two enzymes have been studied and compared. Moreover, an amino-acid analysis has been carried out for rat brain aldolase C.Within experimental errors, the two enzymes appear to be identical.