Enzymes are biological catalysts (also known as biocatalysts) that speed up biochemical reactions in living organisms, and which can be extracted from cells and then used to catalyse a wide range of commercially important processes. This chapter covers the basic principles of enzymology, such as classification, structure, kinetics and inhibition, and also provides an overview of industrial applications. In addition, techniques for the purification of enzymes are discussed.

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Over the past twenty years or so, glow discharge mass spectrometry (GDMS) has become the industry standard for the analysis of trace elements in metals and semiconductors. A review of its history is followed by a picture of the present situation and a look to where the future may lie. Applications are summarised, including the ability of GDMS to offer depth-resolved data and non-conductor analysis, and the well-documented quantitative nature of the results is reviewed. The effects resulting from the physical properties of the analyte material are discussed at length. Finally, recent work such as "fast flow" sources and pulsed glow discharges is reviewed.

Investigations were carried out using immobilized Chlorella cells to determine the diameter, compressibility, tolerance to phosphate chelation, and ability to retain algal cells during incubation of various alginate beads. These physical bead characteristics were found to be affected by a variety of interactive factors, including multivalent cation type (hardening agent) and cell, cation, and alginate concentration, the latter exhibiting a predominant influence. The susceptibility of alginate beads to phosphate chelation was found to involve a complex interaction of cation type, concentration, and pH of phosphate solution. A scale of response ranging from gel swelling to gel shrinking was observed for a range of conditions. However, stable calcium alginate beads were maintained in incubation media with a pH of 5.5 and a phosphate concentration of 5 microM. A preliminary investigation into cell leakage from the beads illustrated the importance of maintaining a stable gel structure and limiting cell growth to reduce leakage.

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In latter years the growth of methods has led to a detailed understanding of the concentration and distribution patterns of electrolytes and water in the extracellular liquids. More recently attention has been directed toward the intracellular phase. The greater bulk of observations has been concerned with the most abundant intracellular cation, potassium. Much less is known about magnesium, second only to potassium with respect to concentrations within cells.There are many indications of the intimate role which magnesium plays in modulating neural excitability and muscular contraction (1-7); in catalysing several enzymic processes concerned with the transfer, storage and utilization of energy (8)(9)(10)(11)(12)(13)(14) ; and, perhaps, in the adjustment of overall bodily economy reflected in temperature regulation and hibernation (15,16). Yet little is known of the patterns of its ebb and flow into and out of cells, or, indeed, of the concentrations obtaining within cells during most diseased states. This study was begun in order to discover what changes, if any, occurred in the magnesium content of skeletal muscle during certain clinical states marked by disturbances of electrolyte metabolism and accompanied occasionally by asthenia.For purposes of reference, concentrations of magnesium and of potassium in muscle were measured at the same time. It soon became apparent that even in the most diverse states of disease, as well as in health, an extraordinarily fixed relationship obtained in muscle between concentra-

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Comparison with earlier studies indicates that compliance with recent GDC standards is generally improving, though whether the pace of improvement is seen as acceptable or not is something that policymakers and regulatory authorities may need to consider further.