472
ERIC E. CONN
tions. Phosphorylation has also been observed in particles prepared
from the water mold Allomyces macrogynus (218).
Oxidative phosphorylation has been observed in a few microorganisms. Chief among these is Azotobacter vinehndii, where phosphorylation was observed first in cell-free extracts (219). Later work involved
the isolation and study of small particles from this organism (107, 110).
The P/O ratios obtained with these preparations are low in comparison
with those obtained with animal mitochondria; moreover, the phosphorylation is largely insensitive to dinitrophenol. Phosphorylation has also
been obtained with extracts from Mycobacterium phlei and Corynebacterium creatinovorans (112). The P/O ratios in these studies were
higher; values greater than 1.0 were obtained with several Krebs cycle
substrates. The phosphorylations were uncoupled by dinitrophenol.
Cell-free extracts of Alcaligenes faecalis support oxidative phosphorylation during the oxidation of DPNH (220, 221). It is possible to fractionate the extract into three components, a particulate DPNH oxidase
fraction and two soluble fractions, one of which is labile to heat. Recent
work suggests that the heat-stable component may be a polynucleotide
of the ribonucleic acid type (220, 222). Although low P/O ratios
(0.1-0.3) have been encountered in these studies, there is evidence to
suggest that fewer cytochrome components are present in the oxidation chain responsible for the oxidation of DPNH (223). This in turn
implies that fewer points of conservation of energy exist in the respiratory chain of these organisms.
IV. Other Respiratory Pathways
The possible existence of respiratory chains not involving the cytochromes has been investigated to the greatest extent in plant tissues.
Lack of information concerning the cytochromes in plants stimulated
searches for other terminal oxidases. Enzymes (and their substrates)
which transferred · electrons to molecular oxygen were known to be
widespread in plants. In addition, the fact that the respiration of some
plant tissues is relatively insensitive to carbon monoxide or cyanide indicated that a terminal oxidase other than cytochrome oxidase was
functioning in those tissues. The large amount of information on this
subject has been described and evaluated in several reviews (224-227).
The studies on terminal oxidases in higher plants have coincided with
experiments which sought to determine the relationship of these enzymes
to processes such as growth, water uptake, and ion accumulation which
require energy. For example, the growth of sections of pea epicotyls and
Avena coleoptiles was inhibited 90% in CO:0 2 mixtures of 20:1 (228).
This inhibition was completely reversed in light in the case of the
ERIC E. CONN
tions. Phosphorylation has also been observed in particles prepared
from the water mold Allomyces macrogynus (218).
Oxidative phosphorylation has been observed in a few microorganisms. Chief among these is Azotobacter vinehndii, where phosphorylation was observed first in cell-free extracts (219). Later work involved
the isolation and study of small particles from this organism (107, 110).
The P/O ratios obtained with these preparations are low in comparison
with those obtained with animal mitochondria; moreover, the phosphorylation is largely insensitive to dinitrophenol. Phosphorylation has also
been obtained with extracts from Mycobacterium phlei and Corynebacterium creatinovorans (112). The P/O ratios in these studies were
higher; values greater than 1.0 were obtained with several Krebs cycle
substrates. The phosphorylations were uncoupled by dinitrophenol.
Cell-free extracts of Alcaligenes faecalis support oxidative phosphorylation during the oxidation of DPNH (220, 221). It is possible to fractionate the extract into three components, a particulate DPNH oxidase
fraction and two soluble fractions, one of which is labile to heat. Recent
work suggests that the heat-stable component may be a polynucleotide
of the ribonucleic acid type (220, 222). Although low P/O ratios
(0.1-0.3) have been encountered in these studies, there is evidence to
suggest that fewer cytochrome components are present in the oxidation chain responsible for the oxidation of DPNH (223). This in turn
implies that fewer points of conservation of energy exist in the respiratory chain of these organisms.
IV. Other Respiratory Pathways
The possible existence of respiratory chains not involving the cytochromes has been investigated to the greatest extent in plant tissues.
Lack of information concerning the cytochromes in plants stimulated
searches for other terminal oxidases. Enzymes (and their substrates)
which transferred · electrons to molecular oxygen were known to be
widespread in plants. In addition, the fact that the respiration of some
plant tissues is relatively insensitive to carbon monoxide or cyanide indicated that a terminal oxidase other than cytochrome oxidase was
functioning in those tissues. The large amount of information on this
subject has been described and evaluated in several reviews (224-227).
The studies on terminal oxidases in higher plants have coincided with
experiments which sought to determine the relationship of these enzymes
to processes such as growth, water uptake, and ion accumulation which
require energy. For example, the growth of sections of pea epicotyls and
Avena coleoptiles was inhibited 90% in CO:0 2 mixtures of 20:1 (228).
This inhibition was completely reversed in light in the case of the