Compartmentation of glutamate metabolism in brain. Evidence for the existence of two different tricarboxylic acid cycles in brain

1. (14)C from [1-(14)C]glucose injected intraperitoneally into mice is incorporated into glutamate, aspartate and glutamine in the brain to a much greater extent than (14)C from [2-(14)C]glucose. This difference for [1-(14)C]glucose and [2-(14)C]glucose increases with time. The amount of (14)C in C-1 of glutamate increases steadily with time with both precursors. It is suggested that a large part of the glutamate and aspartate pools in brain are in close contact with intermediates of a fast-turning tricarboxylic acid cycle. 2. (14)C from [1-(14)C]acetate and [2-(14)C]acetate is incorporated to a much larger extent into glutamine than into glutamate. An examination of the time-course of (14)C incorporated into glutamine and glutamate reveals that glutamine is not formed from the glutamate pool, labelled extensively by glucose, but from a small glutamate pool. This small glutamate pool is not derived from an intermediate of a fast-turning tricarboxylic acid cycle. 3. It is proposed that two different tricarboxylic acid cycles exist in brain.     

Transduction of Merodiploidy: Induced Duplication of Recipient Genes

Escherichia coli PB160, which carries a tandem duplication with the gene order metB(+)argH(-)su(159) (+)thi(+): metB(+)argH(+)su(159) (-)thi(+), was used to study the mechanism of P1 transduction of genes in the duplicated region. Transduction of the su(159) (+) allele contained within the duplicated segment yields two kinds of su(159) (+) recombinants: 91% are haploid su(159) (+) and 9% are su(159) (+)/su(159) (-) merodiploids. The duplication in these merodiploid transductants includes the metB locus; however, both copies of the metB locus usually are derived from the recipient. Thus, the requirements for transduction of the "condition of merodiploidy" appear to be the cotransduction of the repeat point (the region where the duplication begins to repeat itself) and, of course, the selected marker (in this case su(159) (+)). A mechanism whereby two recipient chromosomes interact with the transduced "repeat point" region to regenerate the tandem duplication is implicated. It appears that a duplication much larger than the quantity of genetic material carried by a P1 phage can be produced in a transductant.