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Microbodies were first reported at the ultrastructural level in the proximal convoluted tubule of mouse kidney by Rhodin in 1954 (1) and in hepatic parenchymal cells by Rouiller and Bernhard in 1956 (2) at about the time The Journal of Cell Biology was established . They were reported in plants by Porter and Caulfield in 1958 (3) and by Mollenhauer et al. in 1966 (4) . Microbodies are now recognized as ubiquitous subcellular respiratory organelles in eukaryotic cells . Microbodies from all tissues appear morphologically similar and have similar enzymatic properties, but the metabolic pathways within this subcellular compartment vary, depending upon the tissue . Microbodies (peroxisomes and glyoxysomes) were one of the last major subcellular compartments to be recognized, and it was not until the end of the 1960s that their significance was established by several reviews . Most important were the following two summaries: "Peroxisomes (Microbodies and Related Particles)" by de Duve and Baudhuin in 1966 (5), and "The Peroxisome: a New Cytoplasmic Organelle" by de Duve in 1969 (6) . The Nobel Prize that de Duve received was based on his pioneering work in the discovery and isolation of subcellular organelles, such as microbodies. Material in these two papers is essential reading for new students in the field . Also in 1969, the morphological literature was assembled into a book, Microbodies and Related Particles by Hruban and Rechcigl (7), which summarized the evidence for the widespread distribution of the particle . Another landmark in 1966, also from de Duve's group (8), was the development of procedures for isolating microbodies . The first research symposium, "The Nature and Function of Peroxisomes (Microbodies, Glyoxysomes)," was held in 1969 (9) .Recently there has been such a proliferation of papers about the many aspects of microbodies that in this article we cite only reviews or use only an initial reference to a specific subject. Some of the general reviews are on development and enzymatic content (10), microbodies in leaves (11-13), germinating seeds (14, 15), algae (16), fungi (17), and protozoa (18); other reviews will be cited with specific topics . Nevertheless, we have little knowledge today of the physiological role of microbodies in cellular metabolism . Properties and characteristics of microbodies are still incompletely described, and much of the recent literature has not been confirmed or well established by the few biologists working in this field .

Membrane-permeable and impermeable inhibitors of carbonic anhydrase have been used to assess the roles of extracellular and intracellular carbonic anhydrase on the inorganic carbon concentrating system in Chlamydomonas reinhardtii. Acetazolamide, ethoxzolamide, and a membrane-impermeable, dextran-bound sulfonamide were potent inhibitors of extracellular carbonic anhydrase measured with intact cells. At pH 5.1, where CO2 is the predominant species of inorganic carbon, both acetazolamide and the dextran-bound sulfonamide had no effect on the concentration ofCO2 required for the half-maximal rate of photosynthetic 02 evolution (Ko4C021) or inorganic carbon accumulation. However, a more permeable inhibitor, ethoxzolamide, inhibited CO2 fixation but increased the accumulation of inorganic carbon as compared with untreated cells. At pH 8, the K165(CO2) was increased from 0.6 micromolar to about 2 to 3 micromolar with both acetazolamide and the dextranbound sulfonamide, but to a higher value of 60 micromolar with ethoxzolamide. These results are consistent with the hypothesis that CO2 is the species of inorganic carbon which crosses the plasmalemma and that extracellular carbonic anhydrase is required to replenish CO2 from HC03-at high pH. These data also implicate a role for intracellular carbonic anhydrase in the inorganic carbon accumulating system, and indicate that both acetazolamide and the dextran-bound sulfonamide inhibit only the extracellular enzyme. It is suggested that HC03-transport for internal accumulation might occur at the level of the chloroplast envelope.

2-C-Carboxy-D-ribitol 1,5-bisphosphate and 2-C-carboxy-D-arabinitol 1,5-bisphosphate have been synthesized, purified, and characterized. In the presence of Mg2+, 2-C-carboxy-D-arabinitol 1,5-bisphosphate binds to ribulose-1,5-bisphosphate carboxylase/oxygenase by a two-step mechanism. The first, rapid step is similar to the binding of ribulose 1,5-bisphosphate or its structural analogues. The second step is a slower process (k = 0.04 s-1) and accounts for the tighter binding of 2-C-carboxy-D-arabinitol 1,5-bisphosphate (Kd less than or approximately to 10(-11) M) than of 2-C-carboxy-D-ribitol 1,5-bisphosphate (Kd = 1.5 X 10(6) M). Both carboxypentitol bisphosphates exhibit competitive inhibition with respect to ribulose 1,5-bisphosphate. 2-C-(Hydroxymethyl)-D-ribitol 1,5-bisphosphate and 2-C-(hydroxymethyl)-D-arabinitol 1,5-bisphosphate were also synthesized; both are competitive inhibitors with respect to ribulose 1,5-bisphosphate with Ki = 8.0 X 10(-5) M and Ki = 5.0 X 10(-6) M, respectively. Thus, the carboxyl group of 2-C-carboxy-D-arabinitol 1,5-bisphosphate is necessary for maximal interaction with the enzyme. Additionally, Mg2+ is essential for the tight binding of 2-C-carboxy-D-arabinitol 1,5-bisophsphate. A model for catalysis of ribulose 1,5-bisphosphate carboxylation is discussed which includes a functional role for Mg2+ in the stabilization of the intermediate 2-C-carboxy-3-keto-D-arabinitol 1,5-bisphosphate. Mechanistic implications that arise from the stereochemistry of this intermediate are also discussed.

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Ammediol, 2-amino-2-ethyl-l,3-propanediol; EDTA, ethylenediaminetetraacetic acid. more stable than the carboxylase when the protein was stored as an (NH4)2S04 precipitate. The pH optimum of the oxy-