Regulation of Information Metabolism

Inducible Genes turned on by the presence of a substrate for a catabolic (degradafive) pathway. 

Repressible Genes turned off by the presence of a product of a biosynthetic pathway. 

Positive regulators (enhancers) Turn on transcription when a specific effector protein binds to a specific enhancer sequence in the DNA. 

First recombination between D and J segments brings these segments together 

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Regulation of information metabolism occurs at each stage. The net result is that specific proteins can be made when their activities are needed. 

Cell line selection is one of the traditional and effective approaches to enhancing metabolite accumulation, and biochemical studies provide the fundamental information for the intentional regulation of secondary metabolism in plant cells. In a carrot suspension culture regulated by 2,4-dichlorophenoxyace-tic acid, Ozeki et al. [7] found that there was a correlation between anthocyanin synthesis and morphological differentiation for somatic embryogenesis they also demonstrated the induction and repression of phenylalanine ammonia lyase (PAL) and chalcone synthase correlated with formation of the respective mRNAs. Two biosynthetic enzymes, i. e., PAL and 3-hydroxymethylglutaryl-CoA reductase, were also related with shikonin formation in Lithospermum erythro-rhizon cultures [8]. 

In this review we have only dealt with alkaloid biosynthesis in C. roseus the biochemistry of this plant has also been studied in detail for other aspects, such as anthocyanin production, phosphate metabolism, cell growth, and cell division cycle (e.g., ref. 362). Unfortunately, most of the studies concerning the primary metabolism are not linked with those of secondary metabolism. However, one may expect that in the future the studies on secondary metabolism, such as chorismate-derived products (an-thocyanins, benzoic acid derivatives, and alkaloids) and terpenoid-derived products such as the alkaloids, will be integrated. This will eventually allow us a much better insight into the overall biochemistry of the plant. All of the available information makes C. roseus an outstanding model system for the study of the regulation of plant metabolism. 

Thus, the chapters presented here are a microcosm of what the recent completion, or near completion, of various genome projects are enabling biochemists to understand not only about control and regulation of secondary metabolism, and how various pathways relate to each other, but also about its relation to primary metabolism. A major paradigm shift is occurring in the way we need to view secondary metabolism in the future. It is also clear that model systems, such as the ones discussed in the symposium, are providing new information and insight almost faster than we can process it ... 

Mechanisms involved in the regulation of microbial metabolism can be divided into two general classes—those that alter enzyme concentration and those that alter enzyme activity. Each class is comprised of several specific mechanisms which have been extensively studied and well documented. However, the extent to which identical mechanisms contribute to the coordination of metabolism in higher plants has not yet been resolved. Various aspects of this problem have been discussed in recent reviews which should be consulted for detailed information (Trewavas, 1976 Davies, 1979 Miflin, 1977 Ricard t al., 1977 Stewart and Rhodes, 1977 Wallace, 1976). 

The potential existence of futile cycles shows that mass action control would not be adequate. If such potential cycles actually functioned cyclically, the net reaction would be hydrolysis of ATP, and they would not be limited by mass action until the cell s ATP supply had been virtually abolished. More effective controls are evidently necessary. On the basis of current information, it seems unlikely that direct mass action effects play a primary role in the regulation of any metabolic processes. On the other hand, little is known about the regulation of electron transport phosphorylation, and the possibility of relatively simple mass action control of this process has not been ruled out. It would appear, however, that if such mass action controls exist, the limiting substrate is likely to be DPNH rather than ADP or P, since present evidence suggests that glycolysis and the citrate cycle, and thus the supply of DPNH, are tightly controlled. Thus even if mass action effects actually play a significant role in the control of electron transport phosphorylation, they are probably secondary to more flexible controls of other types. 

Allosteric communication consisting of a vectorial transmission of information from one protomer to another is an example of concerted motion in proteins occurring through the close packing of the atoms. The role of the process in modulating the activity by amplification or attenuation of the catalytic response is fundamental for regulation of cell metabolism. 

Apart from these few studies, no information concerning the regulation of the PA biosynthetic enzymes in plants at a molecular level is available. The regulation of PA metabolism by endogenous and exogenous stimuli will be discussed in another section of this chapter (see Section VI). 

Nearly all biological processes involve the specialized functions of one or more protein molecules. Proteins function to produce other proteins, control all aspects of cellular metabolism, regulate the movement of various molecular and ionic species across membranes, convert and store cellular energy, and carry out many other activities. Essentially all of the information required to initiate, conduct, and regulate each of these functions must be contained in... 

Information on which parasite products might regulate infected muscle cell characteristics is unresolved. Parasite proteins will be the focus of this discussion. This focus results in part from general lack of information on other secreted products/metabolic wastes and their potential influences on the host cell. In addition, arguments for cell-permeable parasite products are less compelling, and no clear evidence exists for a bystander effect in which bona fide infected cell characteristics become established in neighbouring, uninfected host muscle cells. 

Information metabolism provides a way to store and retrieve the information that guides the development of cellular structure, communication, and regulation. Like other metabolic pathways, this process is highly regulated. Information is stored by the process of DNA replication and meiosis, in which we form our germ-line cells. These processes are limited to specific portions of the cell cycle. Information is retrieved by the transcription of DNA into RNA and the ultimate translation of the signals in the mRNA into protein. 

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