The major developments during the past year have been along the fol1ow ing lines: (a) A renewal of interest in several alternate metabolic pathways, including the Warburg-Lipmann-Dickens pathway for glucose oxidation, via pentose, the Thunberg mechanism for formation of 4-carbon acids by con densation of two 2-carbon units, and the methyl glyoxalase system. (b) The establishment of the structure of two new coenzymes, one concerned in the galactose-glucose transformation, and the other, coenzyme A, concerned in the transfer of acyl groups. Acety!coenzyme A appears to be the long-sought "active acetate." (c) The development of the concept that dehydrogenases can participate in electron transfer, without dissociation of the "bound" pyridine nucleotides. (d) Advances in the understanding of the mechanism of heterotrophic and photosynthetic carbon dioxide assimilation. (e) Solubili zation and purification of certain enzymes of the citric acid cycle, which have heretofore been available only in particulate form. REVERSIBLE DEGRADATION OF CARBOHYDRATESTO 3-CARBON ACID STAGE THE OVER-ALL PROCESSAlternate pathways ' of degradation.-The term "glycolysis," usually ap plied to this process, is avoided here, because it is planned to consider in this section not only the reactions of the Embden-Meyerhof (E-M) scheme, but also the reactions of the Warburg-Lipmann-Dickens (W-L-D) scheme, which leads to the formation of triose by an alternate pathway. The former path way is usually regarded as anaerobic, and the latter as aerobic. A selective effect of a given inhibitor (e.g., iodoacetate or fluoride) on anaerobic metabo lism, without a corresponding depression of glucose oxidation, has been in terpreted as supporting the existence of two pathways for degradation of hexoses. More direct evidence for the occurrence of the W-L-D scheme in both animal and plant cells is described in a later section.The relative quantitative importance of these two pathways for glucose oxidation remains to be assessed. It may be worthy of note that whereas the E-M scheme provides, per molecule of hexose, two three-carbon fragmen ts 1 This review covers the period'from January 1st to December 31st, 1950.2 The foJlowing abbreviations are used throughout: ATP, ADP, and AMP for adenosinetri-, di-, and mono-phosphate; DPN and TPN for di-and triphosphopyri dine nucleotides; FAD for flavine adenine dinucleotide; P for phosphate, and ",P for energy-rich phosphate.'