Ribulose biophosphate carboxylase from Thiobacillus A2. Its purification and properties

Ribulose bisphosphate carboxylase (EC 4.1.1.39) from Thiobacillus A2 has been purified to homogeneity on the basis of polyacrylamide gel electrophoresis and U.V. analysis during sedimentation velocity studies. The enzyme had an optimum pH of about 8.2 with Tris-HCl buffers. The molecular weight was about 521000 with an Srel. of 16.9. Km for RuBP was 122 muM, for total "CO2" it was 4.17 mM, and for Mg2+ 20.0 muM. The absolute requirement for a divalent cation was satisfied by Mg2+ which was replaceable to a certain extent by Mn2+. Activity was not significantly affected by SO(2-4), SO(2-3), or S(2)O(2-3) at 1.0 mM. At this concentration S(2-) caused a 27% stimulation. All mercurials tested were inhibitory. pHMB was the most potent causing about 60% inhibition at 0.04 mM. This inhibition was reversible by low concentrations of cysteine. Cyanide was also inhibitory. Its mode of inhibition with respect to RuBP was un-competitive and with a Ki of 20 muM. Lost activity could be restored partially by GSH or Cu2+. Although azide at the concentration tested had no significant effect on enzyme activity, 2, 4-dinitrophenol at 1.0 mM caused 91% inhibition. Finally, activity was also affected by energy charge.

Physical properties and metabolite regulation of ribulose bisphosphate carboxylase from Thiobacillus A2

Purified ribulose-bisphosphate carboxylase (EC 4.1.1.39) was strongly and equally inhibited either by ADP or GDP and to a lesser extent by IDP. AMP or ATP exerted little effect on activity. Inhibition by the nucleotide diphosphates was competitive with respect to RuBP and non-competitive with respect to "CO2" and Mg2+, respectively. Treatment of the enzyme with urea or guanidine-HCl resulted in rapid loss of activity that was not restored by dialysis even in the presence of Mg2+ and cysteine. Sodium dodecyl sulfate electrophoresis of 8.0 M urea treated enzyme revealed the presence of a fast-moving (small) sub-unit with molecular weight 14150 and a slower moving (large) sub-unit with molecular weight 68000. Examination of native enzyme by sodium dodecyl sulfate electrophoresis gave sub-units of 13700 and 55500 respectively. The amino acid content standardized to phenylalanine was essentially similar to that from other sources. Arrhenius plots showed a "break" at 29 degrees C with an Ea of 12.34 kcal per mole for the steeper part of the curve and a deltaH of 11.43 kcal per mole while for the less steep region, the Ea was 1.04 kcal per mole and the deltaH 1.92 kcal per mole.

Wind Tunnel Simulations of Light and Dark Streaks on Mars

Wind tunnel experiments have revealed a characteristic flow field pattern over raised-rim craters which causes distinctive zones of aeolian erosion and deposition. Comparisons of the results with Mariner 9 images of Mars show that some crater-associated dark zones result from wind erosion and that some crater-associated light streaks are depositional.

Anaesthesia for thyroid surgery

The principles involved in preoperative assessment and management of the patient who is to undergo thyroidectomy are discussed.

The techniques of anaesthesia that have been found most successful for thyroidectomy at The Royal North Shore Hospital of Sydney are described. The effectiveness of these techniques is indicated by reference to the complications found following review of 200 consecutive thyroidectomies.

Sensory Deprivation and Visual Speed: An Analysis

Speeds of moving objects were markedly underestimated by human observers after prolonged patternless visual stimulation. Even greater underestimation followed exposure to a "noisy" visual field; on the other hand, exposure to a hyperstable field caused overestimation. The effects of external visual noise simulate those of deprivation; this finding suggests that similarly disordered but spontaneous neural discharge dominates the visual nervous system in deprivation.