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The Δ 5 - β -3-OH sterols, cholesterol, ergosterol, sitosterol, and stigmasterol, reversed the antifungal activity of pimaricin on S. cerevisae while mevalonic acid, squalene and lanosterol were inactive in this respect. Several explanations for this effect were discussed.

The 2-, 4-, and 6-pyridones related to 1-methylnicotinonitrile have been synthesized and their properties compared. The 4-pyridone is a new compound and the 2-pyridone has not been obtained synthetically before. The 4- and 6-pyridones are identical to two of the products obtained from enzymatic oxidation of nicotinonitrile methiodide.

The crude extract of pyridinium oxidizing enzymes from Ricinus communis seedlings was resolved into three enzyme entities by DEAE column chromatography. Their optimal pH, temperature stability, activation energies and substrate specificities are similar. Analysis of their enzymatic products have shown that each of these enzymes catalyses the oxidation of 1-methyl-nicotinonitrile perchlorate to form 4- and 6-pyridones.

Pyridinium oxidase B from Ricinus communis, initially separated by DEAE cellulose column chromatography, was further purified. The fraction with the highest activity from Ecteola cellulose column still showed a trace of impurities in polyacrylamide gel electrophoresis. Molecular weight estimation by sucrose gradient ultracentrifugation showed that pyridinium oxidase B has an apparent molecular weight of approximately 250,000. The rate of 4- and 6-pyridone formation in the catalytic process was studied. The ratio of the 6-pyridone to 4-pyridone ranged from 3·5 to 4·1. The Km for 1-methyl-nicotinonitrile perchlorate was found to be 5 × 10−4 M for pyridinium oxidase B, and it decreased with increasing pH. An approximate pKa of 9:9 was obtained for the ionizing group involved in the enzymatic reaction. The Km values for its substrate analogues, except 1-methyl-3-acetyl pyridinium, were found to be the same. However, the value of Vm increased as the dipole moment of the 3 substituent increased. The present evidence indicates that the positively charged quaternary nitrogen is necessary for the enzyme-substrate binding, and a strong electron withdrawing group will enhance the oxidation reaction. The enzyme resembles aldehyde and xanthine oxidase in its ability to oxidize a wide variety of nitrogenous compounds.

A crude enzyme system prepared from young castorbean seedlings catalyzes the oxidation of 1-methylnicotinonitrile to the corresponding 4- and 6-pyridones. The implications of this reaction for the biosynthesis of the alkaloid ricinine are considered. Other pyridone alkaloids might be formed by similar reactions.

When dilute aqueous solutions of liver alcohol dehydrogenase were exposed to X-irradiation, there was much more inactivation in the presence of bicarbonate buffer than in phosphate buffer or in distilled water. The effect was not due to the action of any stable intermediates produced by irradiation of bicarbonate buffer, nor does it seem likely that enzyme is converted by irradiation to some long-lived metastable state whose destruction is precipitated by the presence of bicarbonate. Enzyme and bicarbonate must be present simultaneously for the effect to be observed. Several other enzymes have been investigated in this regard, and possible mechanisms discussed.

At least seven species ( Chrozophora plicata, Jatropha gossypifolia, Ricinus communis, Tragia involucrata, Trewia nudiflora, Acalypha hispida, Synadenium grantii ) in the family Euphorbiaceae have shown enzymatic oxidizing activity on salts of 1-methyl-nicotinotrile. 4- and 6-pyridones were shown to be the enzymic products in vitro for both Trewia nudiflora and Ricinus communis .

The responses of common purslane (Portulaca oleracea L.) plants to 2-methoxy-3,6-dichlorobenzoic acid (dicamba) were found to be similar in many respects to ethylene fumigation effects. Dicamba and ethylene increased the permeability of cell membranes in purslane tissues. An increased efflux of electrolytes was observed in the bending region of the stems of dicamba-treated plants. Epinastic leaves after dicamba (10 micrograms) and ethylene (microliter per liter) treatments showed an increased efflux of rubidium. The permeability effects were observable within 1 day after dicamba or ethylene application. Protein metabolism in purslane leaves was not influenced by dicamba until 2 days after treatment, as indicated by reduced nitrate reductase activity. Inhibition of phenylalanine-U-14C incorporation into protein was observed 3 days after treatment. Ethylene reduced both phenylalanine-U-14C incorporation into protein and nitrate reductase activity within 1 day. Dicamba caused a rapid increase in ethylene production in purslane plants to levels many times greater than those observed in untreated plants. It was concluded that the dicamba-enhanced production of ethylene is responsible for many of the observed effects of the herbicide.

In contrast to a previous report no free arginine, agmatine, or other low-molecular-weight guanido compound could be detected in seeds of Ricinus communis (Euphorbiaceae). A heat-stable, arginine-containing protein was isolated and identified with a previously known allergen.

In spite of the large numbers and great diversity of alkaloid structures, it seems possible now to discern a few general principles that apply to the biosynthesis of many different alkaloids. Some broad theories of alkaloid formation have borne the test of many experimental investigations, some have received no support, some have been refuted, and some newcomers have not yet been tested adequately.

Several alkaloids are postulated to be derived from anthranilic acid. These include some rather simple substituted anthranilic acids, quinolines, and some with condensed ring systems of various types. Some of the parent nuclei of these alkaloids are as follows

Pyrrolizidine alkaloids are based on diols called necines which are esterified at one or both hydroxyl groups with a number of different acids, mostly dicarboxylic acids known as necic acids. Some examples of necines and necic acids are shown in Fig. 12-1. Structural variation among the necines is slight. Only about a dozen are known, and they differ from one another mostly in stereochemistry or degree of hydrogenation. Most of the necic acids have 10 carbon atoms arranged as follows: The acids of Crotolaria spp. differ in having only 6 or 8 carbon atoms, and a few other exceptions are known [1].

High-speed liquid chromatography can provide successful separations of two cinchona alkaloids, four opium alkaloids, or heroin-related narcotics. Poly G-300 is used as the liquid stationary phase. Both mechanical-coating and dynamic-coating techniques are employed; dynamic-coating techniques appear to be advantageous for some cases. With the latter technique the degree of partition and adsorption separation mechanisms can be controlled to facilitate separations which might be difficult otherwise. Quantitative analysis of three rapidly eluting opium alkaloids, at nanogram to microgram levels, is described; reasonable accuracy (± 10% or better) was obtained.

RICININE, the alkaloid of castor bean plants, is of interest since it is one of the very few natural products containing a nitrile group and since, as Leete and Leitz1 have shown, it is biogenetically derived from the vitamin, nicotinic acid. In our studies on the distribution and biogenesis of ricinine we have sought a semi-quantitative analytical method that would permit routine determination of ricinine in a large number of samples of plant tissue without tedious extraction and isolation procedures. Such a goal is hindered since ricinine is neutral and does not react with the usual ‘alkaloidal reagents’.

While knowledge about the metabolism of alkaloids in the plants that synthesize them has only recently begun to be developed, pathways of alkaloid degradation by other organisms have been studied for many years, and in a few cases considerable detail is available. The special interest in this area arises, of course, from pharmacological effects of alkaloids, and therefore most studies relate to mammalian metabolism and to alkaloids of widespread use. It is frequently suggested that administered drugs are metabolically converted to the real physiologically active compounds. The metabolism of drugs is a subject of frequent review articles [1–3]; and since many drugs are either natural alkaloids or structurally related compounds, these reviews often include information pertinent to the present discussion. Where not specifically annotated, information in this chapter has been derived from Refs. [1] and [2]. The metabolism of alkaloids by microorganisms has received less attention than their mammalian metabolism, but there is practical reason for such studies, since products of microbial transformation of alkaloids may in some cases themselves be pharmacologically valuable or serve as intermediates for chemical syntheses.

The above quotation may appear preposterously inappropriate in view of the vast literature on pharmacological effects of alkaloids. However, there is indeed little to relate regarding the biochemistry of these effects. Ultimately, gross effects of alkaloids and other foreign molecules on the behavior of animals must have their explanations in terms of specific molecular interactions and chemical reactions. In the course of its development pharmacology has come from observations of total behavior to observations of gross physiological processes, observations on isolated organs and tissues, and elegant and detailed observations at the cellular level. In very few cases has it started to approach observations at the molecular level. At the present, though, it seems important to suggest some of the problems and difficulties that necessarily attend any such molecular approach and to point to a few areas that seem to show some glimmers of success. Essential aspects of pharmacology are doubtless overlooked in this chapter, and it should probably be regarded as a smattering of things that have been of interest to one biochemist rather than a balanced review. Where references to literature are not given, the reader is referred to the general sources [1–7].

The infra-red spectroscopy of aqueous solutions has been hampered not only by the infra-red absorption of water itself, but also by the difficulty of finding material for absorption cell windows which would be insoluble in water and still sufficiently transparent in the desired region. This problem is particularly irksome to biochemists who are primarily interested in aqueous solutions. Several groups of workers1–4 have been successful in observing infra-red spectra in water solution by using cells sufficiently thin for absorption by water not to be excessive and by choosing materials such as silver chloride, barium fluoride, thallium bromide, etc., for windows. The expense and inconvenience of these special windows has prevented many from benefiting by this powerful technique, so that we have been led to consider the possibility of using polyethylene as a window material for aqueous solutions.