Direct visualization of IMP--GMP:pyrophosphate phosphoribosyltransferase in polyacrylamide gels

Direct visual detection of IMP-GMP: pyrophosphate phosphoribosyl-transferase (HGPRT) activity after separation by polyacrylamide gel electrophoresis has not been easy to achieve. Radiochemical assays have been used but they have the disadvantage of requiring considerable amounts of time before the results are available (1.2). A fluorescence assay that couples inosine 5′-monophosphate (IMP) to IMP dehydrogenase with concomitant formation of NADH has been described (3) but is inconvenient because the coupling enzyme is not commercially available. Bieber (4) has developed a fluorescence assay that can be used for HGPRT detection but it requires that the gels be sliced before they are incubated with the substrate mixture. A rapid, convenient method for visual observation of HGPRT activity would facilitate the study of this enzyme and its variants. In this paper we report the development of such a method based on precipitation of inorganic pyrophosphate, one of the reaction products, with Mn²⁺.     

Purification of the medium-chain/long-chain (COT/CPT) carnitine acyltransferase of rat liver microsomes.

A procedure for the purification of the rat liver microsomal carnitine octanoyltransferase (COT) that catalyzes the reversible formation of medium-chain and long-chain acylcarnitines from acyl-coenzyme A is described. The K0.5 for L-carnitine is 0.6 mM and the K0.5 for both decanoyl-CoA and palmitoyl-CoA is 0.6 microM. The Vmax with decanoyl-CoA is approximately fourfold greater than the Vmax with palmitoyl-CoA. The enzyme is monomeric, sodium dodecyl sulfate-polyacrylamide gel electrophoresis gives a molecular weight of 50,100, and molecular sieving gives a molecular weight of 54,300. Purified COT does not cross-react with either antimitochondrial carnitine palmitoyltransferase or antiperoxisomal COT antibodies. It also does not form a covalent adduct when incubated with etomoxiryl-CoA. Microsomal COT is a different protein than either mitochondrial carnitine palmitoyltransferase or peroxisomal COT.     

Hypoxanthine-guanine phosphoribosyltransferase from beef brain: A trimer

Hypoxanthine-guanine phosphoribosyl isolated from beef brain was reacted with cross-linking reagents in order to establish the number of subunits that constitute the native protein. The results obtained from experiments with dimethyl-suberimidate and gluteraldehyde in the absence and in the presence of substrates all indicate that the native structure is a trimer.     

A sliced gel assay for some enzymes which utilize guanine as substrate

A rapid, reasonably sensitive method is described for the location of guanine aminohydrolase and IMP-GMP: pyrophosphate phosphoribosyl-transferase after separation on analytical polyacrylamide gel electrophoresis. The method involves slicing of the gel and is based on the disappearance of guanine as measured by loss of fluorescence at 345 nm when excited at 285 nm in basic solution.     

The effect of electrical stimulation, fasting and anesthesia on the carnitine(s) and acyl-carnitines of rat white and red skeletal muscle fibres

Time courses for the effect of electrical stimulation, fasting and sampling mode (anesthesia vs decapitation) on the quantitative distribution of carnitine and its esters in fast white and fast red skeletal muscle fibres of rats were determined. Both fibre types responded similarly to electrical stimulation with respect to changes in acetyl- and propionylcarnitine, but the time course was very different. The proportion of esterified carnitine decreased with fasting and anesthesia in both fibres compared to the fed decapitated group. This shift in the acylation state of carnitine was mainly due to the decrease of acetylcarnitine levels. The data show that the use of anesthetics may induce significant quantitative changes in specific acylcarnitine levels, presumably reflecting changes in specific acylcoenzyme A levels.