An enhanced time out is an improved communication process initiated to prevent such surgical errors as wrong-site, wrong-procedure, or wrong-patient surgery. The enhanced time out at my facility mandates participation from all members of the surgical team and requires designated members to respond to specified time out elements on the surgical safety checklist. The enhanced time out incorporated at my facility expands upon the safety measures from the World Health Organization's surgical safety checklist and ensures that all personnel involved in a surgical intervention perform a final check of relevant information. Initiating the enhanced time out at my facility was intended to improve communication and teamwork among surgical team members and provide a highly reliable safety process to prevent wrong-site, wrong-procedure, and wrong-patient surgery.

A mutant, ac i72, of Chlamydomonas reinhardi possessing an altered ribulosebisphosphate carboxylase and unable to grow on minimal medium has been isolated and characterized. Comparison of ribulosebisphosphate carboxylase purified from both wild type and ac i72 strains is given. The enzyme from ac i72 shows alterations in several characteristics : (a) the specific activity is reduced to 35 % that of wild type, (b) the Vfor both substrates is reduced 3-6-fold, (c) the Mg2+ requirement for maximal activity is 3 times greater, (d) the inhibitory effect of C1-is greater, and (e) the isoelectric point is changed (6.0 for wild type and 5.8 for ac i72). However, the ribulosebisphosphate carboxylase from ac i72 is identical to that from wild type with respect to pH requirement, temperature sensitivity, subunit structure, and sedimentation characteristic.Other photosynthetic properties of wild type and ac i72 cells were also compared. C 0 2 fixation in ac i72 in vivo is reduced proportionally to the reduction in activity of the enzyme, but the level of O2 evolution is the, same as in wild-type cells. Photosynthetic electron transport, 70-S ribosome content, and chlorophyll content are unaltered in ac i72. The chloroplast ultrastructure of ac i72 cells is distinctly different from that of wild-type cells. The inheritance of the mutation is Mendelian.It is well established that Rbu-1 ,5-P2 carboxylase is the primary carbon-fixing enzyme in plants, catalyzing the condensation of Rbu-1,5-P2 and COz. Recent investigations have shown that this enzyme plays an additional enzymatic role, that of an Rbu-1,5-P2 oxygenase [I -41. As such, it acts as the primary photorespiratory enzyme, catalyzing the condensation of Rbu-1,5-P2 and O2 in the formation of phosphoglycerate and phosphoglycolate [l, 31. The relative activities of these two enzymatic functions are dependent upon a competition between C 0 2 and O2 [2,5]. With regard to the complex role that this enzyme plays, it is interesting that Rbu-1 ,5-P2 carboxylase is present in very large amounts in the chloroplasts of plants, composing a major part of the soluble protein of the chloroplast [6]. Also, Rbu-1,5-P2 carboxylase is a very large protein of molecular weight 500-600000 and consists of several copies of two nonidentical subunits [7]. The reason for the excess of Rbu-1,5-P2 carboxylase in comparison to other Calvin cycle enzymes and the necessity of such a large and complex molecule is not understood.Abbreviations. Rbu-1,5-P2, ribulose 1,5-bisphosphate; Hepes, N-2-hydroxyethylpiperazine-N'-2-ethane sulfonate.Enzyme. Ribulose 1.5-bisphosphate carboxylase (EC 4.1.1.39).Recent evidence suggests that both the Rbu-1 ,5-P2 carboxylase and the Rbu-l,5-P2 oxygenase activities are a function of the large subunit and that the small subunit may perform a regulatory function [8-111. In this paper we describe the rationale behind the method of selection of mutants with possible alterations in Rbu-1 ,5-P2 carboxylase and the partial characterization of one such mutant strain, ac i72. The...

A previously described Mendelian mutant of Chlamydomonas reinhardi, ac i72, exhibiting altered ribulosebisphosphate carboxylase activity and unable to grow on minimal medium is examined for changes in ribulosebisphosphate oxygenase activity. The ribulosebisphosphate oxygenase activity of the enzyme purified from both wild type and ac i72 is compared over a pH range from 7.0 to 9.5. Both enzymes exhibit maximum activity at pH 9.0. However, the ac i72 enzyme is twice as active as the wild type enzyme at a physiological pH of 7.0.The studies in vivo of the products of CO, fixation of ac i72 and wild type cells in the presence of high and low 0, concentration shows that due to a lower level of carboxylation, the ac i72 cells fix CO, at half the rate of wild type cells. In ac i72,24 % of the photosynthetically fixed I4C is channelled into the water-soluble fraction as opposed to 6 %in wild type. Thin-layer chromatography of the watersoluble fraction showed extensive accumulation of components of the glycolate pathway in ac i72 as compared to wild type. This indicates that the oxygenase activity of the enzyme prevails in ac i72 in vivo. Since a high concentration of glycolate is toxic to cells of C . reinhardi, the high oxygenase activity of ac i72 provides an explanation for the inability of ac i72 to grow phototrophically even though its rate of CO, fixation is half that of wild type. This toxicity to glycolate is overcome by growth under amber illumination or low 0, concentration.Glycolate was noted among the primary products of photosynthesis by Benson and Calvin [l] and has now been established as one of the main photorespiratory intermediates. However, its mechanism of synthesis has not yet been fully resolved. Several hypotheses have been proposed, one of which suggests that Rbu-l,5-P2 carboxylase acts not only as the primary enzyme in photosynthesis but also as the primary enzyme in photorespiration, and as such functions as Rbu-1,5-P2 oxygenase catalyzing the condensation of Rbu-1,5-P2 and 0, to form phosphoglycerate and phosphoglycolate [2 -51. A specific phosphoglycolate phosphatase, known to be present in the chloroplast, then catalyzes the production of glycolate from phosphoglycolate [6,7]. This scheme, which involves a competitive reaction between C 0 2 and 0, for the same enzyme [3,8], provides an explanation for the Warburg effect of 0, inhibition of photosynthesis and stimulation of photorespiration, the direct relationship between rates of photosynthesis and photorespiration, the light dependence of photo-' respiration and a site of O2 uptake in photorespiration.The oxygenase function of Rbu-1 ,5-P, carboxylase has been demonstrated in the following ways: (a) the two activities copurify to electrophoretic homogeneity [4], (b) the oxygenase activity, as measured by O2 uptake, is dependent upon Rbu-1,5-P2, 02, and enzyme [4], (c) kinetic studies show the competitive nature of O2 and C 0 2 in both carboxylase and oxygenase reactions [8], (d) the catalytic activity of both reactions resides in the larg...