Endogenous metabolism of filamentous fungi.

Among the filamentous fungi the rate of the endogenous respiration, which often is a useful measure of endogenous metabolism, usually is high as compared to the total respiration in the presence of exogenous substrates. This feature is not limited to the fungi alone and may be found under certain conditions in bacteria (Dawes and Holms, 1958) and in animal tissues as well (Allen et al., 1955). Two techniques have been used to determine the status of the endogenous respiration during concurrent utilization of externally furnished substrates: Barker’s indirect manometric method (1936) and the more direct isotopic methods involving either the use of unif ~rmly-C~~-labeled cells and an unlabeled substrate (Bums, 1949) or unlabeled cells and an ~ninformly-C~~-labeled substrate ( Blumenthal, Koffler, and Heath, 1957). In the indirect manometric method, which is based on the premise that over a wide range of substrate/cell ratios a relatively constant proportion of the substrate is oxidized and assimilated, data corrected for the endogenous respiration are compared with uncorrected data. The practice which gives more constant values is considered to be correct even though the basic assumption has not been adequately tested (Blumenthal et d., 1957). A number of modifications of the indirect manometric method have appeared differing in the manner in which the level of the endogenous respiration is varied while keeping the substrate concentration constant (Clifton, 1937; Doudoroff, 1940; Syrett, 1951 ) . With any form of the manometric technique, only an “either-or” decision can be made and, as noted by Barker ( 1936 ) , values for the amount of assimilation are obtained that are just as constant when corrected for the endogenous respiration as when they are not so corrected. The conclusions reached with the indirect manometric have sometimes disagreed with results of the more direct isotopic techniques. Examples of this disagreement can be found in Penicillium chrysogenum (Blumenthal et al., 1957), ChZoreZla vulgaris (Syrett, 1951; Moses and Syrett, 1955) and Euglena gracilis (Danforth and Wilson, 1961 ) . With acetate-grown cells of P. clirysogenui~ the conclusions from both forms of the isotopic technique were in disagreement with the manoinetic results only when acetate was a substrate. In the studies with P . chrysogenuin, we determined the influence of glucose or acetate on the endogenous respiration of mycelium grown with either acetate or glucose as the carbon source. From the results of these experiments it was concluded that the endogenous respiration of glucose-