Our research program on the enzymes hemoglobin and carbonic anhydrase in blood continues to have two major aims. The first is a thorough understanding of the electronic structures, involving both the energy levels and electron distributions, associated with the two enzymes. The second is to understand from an electronic structure point of view, the processes of biological importance that they are associated with. The two aims are of course interrelated, since to be able to obtain insight into the electronic processes that accompany the biological functions of an enzyme, it is important to obtain a good description of its active site. The electronic structures for these systems obtained by ab initio procedures are being tested by their ability to explain associated magnetic and hyperfine properties of these systems. The systems we shall be investigating in the planned research projects, involving the broad field of the electronic structure and properties of hemoglobin and its derivatives and the understanding of the factors influencing cooperativity, are nitrosylhemoglobin, cobaltglobin and deoxy- and oxy-hemoglobin. In the area of enzymes involved in the hydrolysis of carbon dioxide we shall concentrate on the electronic structure and properties of HCAB. Among the properties that we shall be studying to make comparisons with experimental data are magnetic susceptibility, g-shift tensors, magnetic hyperfine interactions, nuclear quadrupole interactions and barrier heights for dissociation of oxygen from hemoglobin and related systems. The changes produced in these properties by the effects of temperature and modifying agents like IHP will also be studied. In the case of hemoglobin systems, we shall attempt to understand from an electronic point of view the basis for changes in atomic configuration associated with the heme unit that result from heme-protein interactions important for the process of cooperativity in oxygen bindings. For the HCAB system, the overall aim of our studied will be the understanding, again from an electronic point of view, of the mechanism for the catalytic action of this enzyme on the hydrolysis of carbon dioxide. We shall also attempt to make significant improvements in the procedures currently in use for the interpretation of electronic properties of these systems, particularly for magnetic and nuclear quadrupole hyperfine interactions and g-shift tensors.