Specific deficit in the synthesis of 6-sulfoquinovsyl diglyceride in Chlorella pyrenoidosa.

It was found that when Chlorella pyrenoidosa was grown on cysteine as the sole sulfur source, it lost the ability to grow photoautotrophically. When grown in the presence of glucose, cysteine-grown cells displayed a doubling time in the light or dark of 45 h, which is identical to that of cells grown on glucose and SO4 in the dark. This suggests that cells grown on cysteine as sole sulfur source can only grow heterotrophically. In support of this hypothesis, it was found that cysteine-grown cells were defective both in vivo and in vitro in CO2 fixation, although O2 evolution in such cells was normal. Assays of the enzymes of the Calvin cycle indicated that the deficit in CO2 fixation could be ascribed to a lowered phosphoribulokinase activity. A total lipid analysis of Chlorella grown on cysteine revealed that such cells showed a 100-fold deficiency in the purportedly chloroplast-associated 6-sulfoquinovsyl diglyceride. This agrees with earlier reports that cysteine could not serve as a precursor of sulfolipid in Chlorella. No other polar lipid was affected. Large amounts of triglyceride, however, were found in cysteine-grown cells. The biosynthesis of triglyceride provides a means of utilizing reduced nicotinamide adenine dinucleotide reducing equivalents not being used for CO2 fixation.

Enzymatic synthesis of 2-O-alpha-D-mannopyranosyl-methyl-alpha-D-mannopyranoside by a cell-free particulate system of Mycobacterium smegmatis.

A cell-free particulate enzyme preparation of Mycobacterium smegmatis ATCC 607 catalyzed the transfer of labeled mannose from GDP[14C] mannose to methyl-alpha-D-mannopyranoside (an exogenously added acceptor) to form a product that was characterized to be 2-O-alpha-D[14C] mannopyranosyl-methyl-alpha-D-mannopyranoside. This transmannosylase activity was specific for both the sugar nucleotide donor and methyl monosaccharide acceptor. The reaction was stimulated by the addition of various metal ions and had a pH optimum of 6.0. The apparent Km of this transmannosylase reaction for methyl-alpha-D-mannopyranoside was 35 mM. The possible relationship between this "artificial" mannosyl-transfer system and the "natural" system which leads to the formation of the oligomannosides and glycoproteins is discussed.