Kinetics of phosphate incorporation into adenosine triphosphate and guanosine triphosphate in bacteria

Escherichia coli cells were labeled with (33)PO(4) for several generations and then (32)PO(4) was added, samples were taken at various times, and adenosine triphosphate (ATP) and guanosine triphosphate (GTP) were purified from an acid extract. The ratio of (32)P/(33)P in each of the six phosphate species was determined and compared to the ratio expected at isotopic steady state. The rate constants of the simplest network of pools which could explain the data, and were consistent with metabolic pathways, were then calculated. In the range of times studied (30 to 3,000 s at 21.5 C) the following generalizations can be made. (i) The gamma-phosphate at ATP requires 2,200 s to achieve 50% of its final specific activity and behaves as if it were exchanging with another species 4.4 times as large, with this other species turning over in 540 s. (ii) The beta-phosphate of ATP and the gamma-phosphate of GTP are in equilibrium with the gamma-phosphate of ATP. (iii) The specific activity of the gamma-phosphate of GTP lags 66 s behind the gamma-phosphate of ATP. (iv) The alpha-phosphates of ATP and GTP have equal specific activities which lag far behind the other four phosphates. A single precursor pool with a turnover time of 416s fits the data best, although a fair fit can be obtained assuming several sequential precursor pools with much shorter turnover times. These findings are consistent with known biosynthetic pathways and the probable flows through them, including the relationship of nucleotide biosynthesis to ribonucleic acid synthesis and turnover.

Grouping and short-term memory: different means and patterns of grouping

Two experiments, concerned with the improving effects of grouping on auditory short-term memory, are described. In the first, temporal grouping was found to improve recall considerably, but non-temporal grouping had a much smaller effect. Temporal grouping reduced the order errors more than other errors; it also changed the pattern of the order errors. Further, it altered the shape of the serial position curve of all errors. In the second experiment, irregular patterns of temporal grouping were found to be inferior to a regular pattern. The results are discussed in terms of the time available for processing previous items during the presentation of a sequence, and the form that this processing may take.

Temporal grouping, rehearsal and short-term memory

The effects of temporal grouping on auditory short-term memory are investigated, using pauses of different lengths to indicate the groups. No quantitative or qualitative differences were found between the shorter and longer pauses. This result, in conjunction with an analysis of the order errors, is used to suggest what kind of processing occurs during the pauses. This processing is selective, recoding the information about order according to position within a group.