C.J. Masters

The developmental multiplicity and isoenzyme status of cavian esterases

Abstract 1. 1. With the aim of clarifying the isoenzyme status of esterases, the developmental and physicochemical properties of these enzymes have been studied in an extensive range of cavian tissues. 2. 2. A total of 24 multiple forms of esterolytic activity have been resolved, and the occurrence of these individual forms in the different tissues inter-related. 3. 3. By means of substrate and inhibitor studies, these heteromorphs have been characterized in four main classes: carboxylesterases, arylesterases, acetylesterases and cholinesterases. 4. 4. All of these classes are heterogeneous—the soluble carboxylesterases existing as 10 separate forms, arylesterases 4, cholinesterases 5, and acetylesterases 5. Each class multiplicity appears to be more extensive than has been previously reported. 5. 5. Further differentiation of the multiple forms in some of these major classes has been achieved on the basis of the physicochemical and developmental parameters utilized. This treatment would appear to implicate at least 12 structural genes in the biosynthesis of the soluble cavian esterases; a multiplicity of control which is, again, considerably in excess of previous estimations for mammalian sources. 6. 6. The significance of the localization and variation of individual esterases is discussed in relation to hormonal influences, cell metabolism and tissue individuality.

On the association of glycolytic enzymes with structural proteins of skeletal muscle

1. The effects of protein concentration and ionic strength on the adsorption of the individual glycolytic enzymes to F-actin and F-actin--trypomyosin--troponin have been studied. 2. Appreciable association was demonstrated under conditions of physiological ionic strength and high protein concentration, and tropomyosin--troponin established as an important and generalized component of these interactions. 3. Phosphofructokinase, aldolase, pyruvate kinase, lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate isomerase were strongly bound under these conditions, while triosephosphate isomerase, phosphoglycerate kinase, phosphoglycerate mutase, enolase and hexokinase displayed less adsorption to the structural proteins. 4. The influence of a number of parameters on the adsorption phenomena was examined. Ca2+ and fructose 1,6-diphosphate increased the adsorption of aldolase, lactate dehydrogenase and pyruvate kinase, while decreasing the adsorption of the enzymes of the constant-proportion group. 5. Of the other major enzymic components of skeletal muscle, creatine kinase, adenylate kinase and malate dehydrogenase showed no adsorption to F-actin--tropomyosin--troponin under the experimental conditions. Some adsorption was evident, however, in the case of aspartate aminotransferase, (NADP) isocitrate dehydrogenase and alpha-glycerolphosphate dehydrogenase. 6. These results have been discussed in relation to their functional significance and the roles of enzyme compartmentation in the cell.

Interactions Between Soluble Enzymes and Subcellular Structur

AbstractSoluble enzymes contribute significantly to the metabolic capabilities of living organisms, but it is becoming increasingly clear that the activities of these enzymes are significantly modified by their interactions with structural components of the cell, and that these interactions may make important contributions to metabolic regulation. In the past, specification of these interactions has been limited by the availability of suitable experimental techniques, but this deficiency is now being rectified and our understanding of these processes is advancing rapidly. Research in this area is moving into a second phase, with the emphasis no longer being focused on demonstrations of the biological reality of these interactions, but directed more towards quantitative aspects of binding, the determination of the characteristics of binding domains, and the theoretical basis of regulatory involvements. All of these aspects are discussed in the present review.

ISOENZYMES AND ONTOGENY

1. In this review, representative data on the nature of enzyme multiplicity and the developmental progressions of multiple enzyme forms have been collected, and the significance of this material has been discussed in relation to gene involvement during tissue differentiation.

Glycolysis — new concepts in an old pathway

SummaryA survey of the existing data on the interactions of glycolytic enzymes with the cellular structure in mammalian tissues has substantiated the occurrence of an extensive degree of such associations in all tissues and during all stages of development. Furthermore, a considerable specificity was evident between the individual multiple forms of the enzymes in relation to these associations.In reviewing these data, a model has been developed which proposes that the glycolytic sequence is best described as consisting of a number of segments in vivo, each segment formed by a cluster of isozymes, many of which can interact with the actin containing filaments of the cytomatrix. The novel features of this segmentation and compartmentation have been described, and evidence has been provided that these phenomena collectively play a key role in meeting the different types of energy requirement in the cytoplasm of divergent cell types, with the wide selection of isozymes in this system offering the potential for increased flexibility and control in this important area of metabolism.

Metabolic control and the microenvironment.

Publisher Summary The concepts of feedback regulation have dominated considerations of metabolic control in cells and tissues in recent years and have markedly advanced our ability to comprehend the nature of self-regulation and the strategic positioning and complex interrelationships of regulatory systems. This marriage of in vitro attributes of control enzymes with in vivo potentialities for regulation is deserving of its frequent nomination as a triumphant example of the analytical approach in biology. The chapter highlights several aspects of the subject that would appear to be worthy of greater attention in this regard—the realities of enzyme and metabolite concentrations in tissues, the feasibility of reversible reactions contributing to control, the concept of sandwiching of regulatory metabolites between controlled enzymes, and the importance of interactions between macro- and micromolecular components.

A comparative study of the multiplicity of mammalian esterases

Abstract 1. 1Multiple forms of soluble esterase activity have been resolved in horse, sheep, ox and possum tissue extracts and sera. 2. 2.By comparing esterase zymograms from different tissues and from different species, it is apparent that the distribution and multiplicity of esterase activity is tissue and species specific. 3. 3.By means of substrate and inhibitor studies, the esterase multiple forms have been characterized into four main classes: carboxylesterases, arylesterases, acetylesterases, and cholinesterases. Each of these can be considered as an isoenzymic group. 4. 4.Evidence is presented for further differentiation of activity within these isoenzymic divisions giving 2 groups of arylesterases, 3 groups of cholinesterases, and 5 groups of carboxylesterases.

Interactions between the bovine milk fat globule membrane and skim milk components on heating whole milk

Heating raw milk at 80 deg C for 2.5-20 min was found to result in compositional changes in the milk fat globule membrane (MFGM). The yield of protein material increased with duration of heating, due to incorporation of skim milk proteins, predominantly beta- lactoglobulin, into the membrane. Lipid components of the MFGM were also affected, with losses of triacylglycerols on heating.

Species specific features of the distribution and multiplicity of mammalian liver catalase

Abstract The multiplicity and subcellular distribution of liver catalase activity have been studied in 10 species of mammals, in order to clarify comparative aspects of the properties of this enzyme. All mammals studied, except mouse, displayed the bulk of liver catalase activity in the cytosol, but the relative proportions of soluble and particulate activity varied quite markedly between species. Sheep, pig, and guinea pig provided the richest sources of supernatant liver catalase; while mouse, rat and pig contained the highest peroxisomal catalase activity. Rabbit, mouse, and rat liver supernatants exhibited 3–4 multiple forms of catalase activity, and displayed an electrophoretic pattern which was distinctly different to that of the aqueous peroxisomal extract. This latter fraction contained a single form of activity of higher anodal migration; a pattern of which was similar to that observed in all fractions of the other species examined. These results may be reconciled with current knowlledge of catalase genetics, subunit structure, and turnover by means of a postulated epigenetic mechanism, involving modifications of the enzyme in rabbit, rat, and mouse liver cytosol.

On the association of glycolytic components in skeletal muscle extracts

Abstract 1. 1. In an extension of previous studies which demonstrated the existence of an association of glycolytic components in extracts of rat skeletal muscle, the properties of this complex have been further investigated. 2. 2. It has been shown that this association of glycolytic enzymes may also be observed in extracts of ovine muscle under physiological conditions of pH and ionic strength, and that the association is sensitive to variations of pH and the concentrations of proteins and specific metabolites such as ATP and fructose 1,6-diphosphate. Furthermore, myosin was identified as a necessary component for complex formation under the experimental conditions. 3. 3. The size of the observed complex of glycolytic enzymes increases with increasing protein concentration; at 52 mg protein/ml, s 20,w values of over 100 are indicated. 4. 4. These data have been discussed in relation to the possible physiological significance of the multi-enzyme association.