All enzymes are not proteins. This statement is justified by
Ribozymes are RNA molecules with catalytic activities, which acts upon phosphodiester bonds in RNA & cause its hydrolysis . RNAs are not protein but meet all the classic criteria of the enzyme, therefore, all enzymes are not protein.
All enzymes do not follow the Michaelis Menton hypothesis
RNAs act as ribozymes
Antibodies take part in the catalysis of many reactions
Metals are involved in attachment to enzymes and catalysts